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Document:	Introduction to VAX-11 Record Management Services
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Introduction to

VAX-11
Record Management Services
Order No. AA-D024C-TE

March 1980

This document contains a general description of the record management services of the VAX/VMS operating system. The information in this document is
introductory in nature; hence, programming techniques are not presented in
this document. Indexed sequential access support is included.

Introduction to

VAX-11
Record Management Services
Order No. AA-D024C-TE

SUPERSESSION/UPDATE INFORMATION: This revised document supersedes
the Introduction to VAX-11 Record
Management Services
(Order No. AA-D0248-TE)
OPERATING SYSTEM AND VERSION:

VAX/VMS V02

SOFTWARE VERSION:

VAX/VMS V02

To order additional copies of this document, contact the Software Distribution
Center, Digital Equipment Corporation, Maynard, Massachusetts 01754

digital equipment corporation . maynard, massachusetts

First Printing, August 1978
Revised, February 1979
Revised, March 1980

The information in this document is subject to change without notice and should not be construed as
a commitment by Digital Equipment Corporation. Digital Equipment Corporation assumes no
responsibility for any errors that may appear in this document.
The software described in this document is furnished under a license and may only be used or copied
in accordance with the terms of such license.
No responsibility is assumed for the use or reliability of software on equipment that is not supplied by
DIGITAL or its affiliated companies.

The postage-prepaid READER'S COMMENTS form on the last page of this document requests the
user's critical evaluation to assist us in preparing future documentation.
The following are trademarks of Digital Equipment Corporation:

DIGITAL
DEC
PDP
DECUS
UNIBUS
COMPUTER LABS
COMTEX
DDT
DECCOMM
ASSIST-11
VAX
DECnet
DATATRIEVE

DECsystem-IO
DECtape
DIBOL
EDUSYSTEM
FLIP CHIP
FOCAL
IND AC
LAB-8
DECSYSTEM-20
RTS-8
VMS
IAS
TRAX

MAS SB US
OMNIBUS
OS/8
PHA
RSTS
RSX
TYPESET-8
TYPESET-11
TMS-11
ITPS-10
SBI
PDT

Contents
Page

Preface

Chapter 1 Introduction
1.1
1.2
1.3
1.4

File Storage Media in General .
What is VAX-11 RMS?
Basic Disk Concepts .
Basic Tape Concepts .

. 1-1
. 1-2
. 1-2
. . 1-7

Chapter 2 VAX-11 RMS Files
2.1
2.2
2.3

2.4

Overview . . . .
File Contents . .
File Organization

. . 2-1
. 2-1
. 2-1

2.3.1
2.3.2
2.3.3

. 2-2
. . 2-3
. 2-4

Record Access Modes . .

. 2-8

2.4.1

Sequential Access.

. 2-9

2.4.1.1
2.4.1.2
2.4.1.3

. 2-9
. 2-9
2-11

2.4.2
2.4.3
2.4.4
2.5

Sequential Organization.
Relative Organization .
Indexed Organization .

Random Access by Key . . . . . . . . .
Random Access by Record's File Address
Record Access Mode Switching

2-11
2-12
2-14

Record Characteristics .

2-15

2.5.1

2-15

Record Formats.
2.5.1.1
2.5.1.2
2.5.1.3
2.5.1.4

2.5.2
2.6

Sequential Access to Sequential Files .
Sequential Access to Relative Files .
Sequential Access to Indexed Files

Fixed-Length Records
Variable-Length Records .
Record Formats and File Organizations .
Variable with Fixed-Length Control Records. .

Storage Structure.

File Size

. . . . . . . .

2-16

2-16
2-16

2-18
2-20
2-20

Chapter 3 File and Record Processing
3 .1
3.2

3.3

Processing Levels . . . .
The File Level Operations

. 3-1
. 3-2

3.2.1
3.2.2

. 3-3
. 3-3

File Protection . .
File Sharing . . .

The Record Level Operations.

. 3-4

3.3.1
3.3.2

. 3-4
. 3-5

Synchronous and Asynchronous Modes of Operation
Record Buffering . . . . . . . . . . . . . . . . .

3.3.3
3.3.4

Record Transfer Modes .
Record Locking .

. 3-5
. 3-6

3.4

Creating the File.

. 3-6

3.5

Processing Records in a File

. 3-7

3.5.1
3.5.2
3.5.3

. 3-8
. 3-8
. 3-8

3.6

Processing Sequential Files
Processing Relative .Files
Processing Indexed Files

Block Input/Output

Glossary

. 3-9
Glossary-I

Index

lndex-1

Figures
1-1 File Extents.
1-2 Files-11 Hierarchy .
1-3 Track and Cylinder Concept
1-4 Interrecord Gaps.
2-1 General Picture of Sequential File Organization .
2-2 General Picture of Relative File Organization .
2-3 Variable-Length Records in Fixed-Length Cells
2-4 Single-Key Indexed File Organization.
2-5 Multiple-Key Indexed File Organization.
2-6 Sequential Access to a Sequential File
2-7 Sequential Read of a Relative File
2-8 Write to a Relative File
2-9 Random Access by Relative Record Number (Key)
2-10 Random Access by Record's File Address .
2-11 Sequential Account File for Dynamic Access
2-12 Using Dynamic Access to Switch Record Access Modes
2-13 Comparison of Fixed- and Variable-Length Records .
2-14 Writing a Variable with Fixed-Length Control Record .
2-15 Reading a Variable with Fixed-Length Control Record .
3-1 Shared File Access .

. 1-3
. 1-4
. 1-5
. 1-8
. 2-2
. 2-3
. 2-4
. 2-6
. 2-7
. 2-9
2-10
2-10
2-12
2-13
2-14
2-15
2-17
2-19
2-19
. 3-1

2-1
3-1

. 2-8
. 3-7

Tables

Record Access Modes and File Organizations
Record Operations and File Organizations .

Preface

Manual Objectives
The Introduction to VAX-11 Record Management Services is an introductory
manual; it is not intended as a guide to the actual programming techniques
required for creating and processing data files. Rather, its purpose is to illustrate the basic file concepts and their application to VAX-11 Record Management Services (VAX-11 RMS). Actual programming techniques are covered
in the VAX-11 Record Management Services Reference Manual.

Intended Audience
This manual aims at all levels of user. If you are a novice, you can use the
manual as a stepping-stone to a basic understanding of record and file management. Experienced users unfamiliar with Digital Equipment Corporation
software can use the manual to gain familiarity with DIGITAL terms and
techniques. Experienced DIGITAL users should find the manual useful because it explains, in general terms, the record management services of the
VAX/VMS operating system.

Structure of this Manual
Information in this document is organized as follows.
• Chapter 1 outlines the basic concepts of disk and tape files, and describes
their interface with VAX-11 RMS.
• Chapter 2 describes the various file organizations, record access modes, and
record formats you can use.
• Chapter 3 outlines the general procedures you can use to create and process
a file, and explains the different modes of file access that a program can use
with VAX-11 RMS.
A glossary of terms appears at the end of this manual.

Associated Documents
VAXNMS provides record management for all supported languages. To use
VAX-11 RMS, VAX-11 MACRO programmers will find. the VAX-11 Record
Management Services Reference Manual and the VAX-11 Record Management Service User's Guide of special interest. Users of higher-level languages
such as VAX-11 FORTRAN, VAX-11 BASIC, or VAX-11COBOL74, should
refer to their particular language manual for the necessary information on
using VAX-11 RMS. The RMS-11 MACR0-11 Reference Manual will be

especially helpful to system programmers using MACR0-11 to employ
RMS-11 facilities. Users of RMS utilities (DEFINE, CONVERT, BACKUP,
DISPLAY, RESTORE, and IFL) will be aided by referring to the RMS-11
Users's Guide. If you are using, or planning to use, RMS-11 on VAXNMS to
build and access files, consult the RMS-11 User's Guide, which describes
RMS-11 concepts and facilities. The VAX-11 Information Directory and Index briefly describes all system documentation, defining the intended audience for each manual and providing a synopsis of each manual's contents.

Summary of Technical Changes
This manual has been revised to reflect VAXNMS support for file sharing for
sequential files with 512-byte fixed-length records.

Chapter 1
Introduction

1.1 File Storage Media in General
As technology has increased, so has the volume of information that must be
saved. Business and industrial concerns, for instance, have compiled many
types of data files about a wide range of subjects. For a long time, all these
data files were stored efficiently on paper in desk drawers and filing cabinets.
But, as these paper files grew, it often took longer to locate the needed data
than to create it in the first place. Storing all of a company's data files on
paper reached the point of diminishing returns.
As the need for saving data increased, the need also arose for a better medium
to store and retrieve data quickly, reliably, and economically. The computer
and computerized filing systems provide such storage media.
At first, computerized files consisted of collections of punched cards.
Cards provide a convenient means of grouping related pieces of information.
This information might represent, for example, a business event, such as a
purchase or sale of office furniture. Or, in the engineering environment, the
information could represent variable equations and data constants related to
stress analysis. This information, grouped on a single card, represents a record
of that event. Records of similar events, grouped together, constitute a file.
As a storage medium, cards have certain advantages. They are easy to add,
delete, or rearrange. However, cards become worn, require physical handling,
and are bulky.
Cards are also relatively slow to process because they allow only sequential file
access. Sequential access means that the search for a record starts at the
beginning of the file and proceeds in order through each record. At times,
when the needed record (or group of records) is near the end of the file, the
search wastes computer processing time.
The introduction of magnetic tape as a storage medium eliminated some of
the disadvantages of cards.
Magnetic tape provides both a storage medium and a means for input/output
(I/0), and its uses have grown along with the needs of the user. Magnetic tape
offers virtually unlimited storage. A large amount of data can fit on a single
tape reel, and you can use as many reels as necessary. Magnetic tape requires
much less storage space than a card file with a comparable amount of data.
But, magnetic tape is limited as a storage medium because, like a card file, it
allows only sequential file access.
In contrast to magnetic tape, disk storage allows direct file access. Direct
access means that the computer can locate the desired record without first

1-1

searching the records that precede it in the file. The time needed to access the
record is relatively independent of the record's location in the file.

1.2 What is VAX-11 RMS?
VAX-11 Record Management Services (VAX-11 RMS) is the file and record
access subsystem of the VAX/VMS operating system for the VAX-11 processor. In combination with the VAX/VMS operating system, VAX-11 RMS
allows efficient and flexible data storage, retrieval, and modification.
When you write a program in one of the supported source languages, you can
select, from among VAX-11 RMS's file organization and record-access modes,
the processing features best suited to your specific application. File organization is the arrangement of data within a file. The file organization and the
storage media together determine which techniques can be used to manipulate data. The record access mode is the manner in which data in the file is
stored and retrieved.
When you create a VAX-11 RMS file, you specify, through either an application program or a VAX-11 utility routine, the file storage medium and the file
and record characteristics. Chapter 2 of this manual outlines VAX-11 RMS
file organizations, record access modes, and record characteristics.
After VAX-11 RMS creates the file according to the specified file and record
characteristics, your application program can store, retrieve, and modify data
records in the file. Chapter 3 of this manual outlines creating, storing, retrieving, and modifying data records in file.
Magnetic tape and disk are the media for storing VAX-11 RMS files. Sections
1.3 and 1.4 below describe the basic concepts of the disk and tape storage
media that VAX-11 RMS uses. VAX-11 RMS also supports unit-record devices, such as line printers, terminals, and card readers in a device-independent fashion. The main purpose of this manual, however, is to provide you with
an introduction to record keeping on magnetic media.

1.3 Basic Disk Concepts
VAX-11 RMS disk files reside on Files-11 disks. Files-11 refers to the logical
structure given to the disk, that is, a hierarchical organization of files, their
data, and the directories needed to gain access to them. The VAXNMS file
system implements the disk structure and provides access control to the files
located on the disk. VAX-11 RMS provides the organization of the files and
method of access to the data within the files.
This section describes the Files-11 structure and defines the terminology
related to it.
The smallest addressable unit of information on a disk is a block. On a
Files-11 disk, a block consists of 512 eight-bit bytes. One or more blocks may
be treated as a single unit for transfer between a Files-11 disk and memory.
Blocks are logically grouped into a cluster, which is the basic unit of disk
space allocation. The system manager or operator determines the number of

1-2 Introduction

blocks in a cluster. This is done when a given disk (a volume) is first prepared
for use (initialized). Allowable cluster sizes are in the range of 1 to 65535
blocks. In general, a disk with a relatively small number of blocks would
usually be given a small cluster size, while larger disks would be given larger
cluster sizes to minimize the overhead for disk space allocation.
Contiguous clusters allocated to a particular file are called an extent. An
extent can contain all or part of a file. The user need not be concerned with
managing extents. This feature is provided by the system. If enough contiguous area is available on the disk, the entire file is allocated as a single extent.
Sometimes, however, not enough contiguous area is available to contain the
entire file. Or sometimes when you initially create a file you may not wish to
reserve the entire required amount of space. Then, when the file is eventually
extended, it is unlikely that the adjacent clusters will still be unallocated,
thus the extension will not occur contiguously. In either of these cases, the file
is divided into two or more parts, and each part is an extent. So, a file can
consist of multiple extents located in separate areas on the disk, as shown in
Figure 1-1.
Figure 1-1: File Extents

Single extent for file A

Figure 1-2 shows the hierarchy of blocks, clusters, extents, and files in the
Files-11 structure.

Introduction 1-3

Figure 1-2: Files-11 Hierarchy

[

Duster

File

Cluster

You can exercise as little or as much control as you desire over the allocation
of space to a Files-11 disk file. At one extreme, you can specify the number of
blocks to be allocated and even give their exact location on the volume. At the
other extreme, you can allow VAX-11 RMS to automatically handle all disk
space allocation details. As an intermediate position, you can specify, for
example, the size of the initial space allocation and the size to be used by
VAX-11 RMS each time the file is extended. In addition, if a file should later
require less space, you can specify that the unused clusters are to be deallocated from the file. These clusters are then available for allocation to other
files on the volume.
When a large amount of file storage space is needed, you can combine several
Files-11 volumes into what is called a volume set. A volume set has the
appearance of one large volume. The different extents of a file can be located
on different volumes in the volume set. In general, you need not specify a
specific volume in the set to locate a file or create a new one, although it is
possible and desirable, for performance reasons, to specify a specific volume to
be used for a particular allocation request.
The smallest item discernible to the Files-11 structure is the block. VAX-11
RMS uses the blocks in the Files-11 structure and allows you to interface with
the individual records in the block.
Other basic terms related to disk structure are track and cylinder.
A track is the collection of blocks at a single radius on one recording surface of
a disk. A track is accessible to a given read/write head position on the disk
device.
A cylinder consists of all tracks at the same radius on all recording surfaces of
a disk.
Because access to any of the blocks in a given cylinder does not require any
movement of the disk's read/write heads, it is generally advantageous to keep
related data blocks in the same cylinder. For this reason, when choosing a

1-4 Introduction

cluster size for a large-capacity disk, a system manager will often select a
cluster size that divides evenly into the cylinder size.
Figure 1-3 illustrates the track and cylinder concept.

Figure 1-3: Track and Cylinder Concept

r--------1

I A track is comprised of
I the area at a single radius

I on one recording surface.

L--------'

,---------,I

I A cylinder consists of

these tracks in the same
I
I radius on all the recording I

L~a~

_____ J

Recording occurs on both
surfaces of each platter. The
extreme top and bottom
surfaces of some disk models
are not used for recording.

A record is the set of data that your program treats as a unit, since it contains
data (about a specific item or event) that you want to manipulate. A record
can be the same size as a block, smaller than a block, or even larger than a
block. Therefore, a block can contain one record, multiple records, or only
part of a record.
The remainder of this section contains a brief explanation of some basic
elements of the Files-11 structure.
A Files-11 structure resides on a volume, which is a physical device medium,
such as a disk pack. A Files-11 volume is an ordered set of 512-byte blocks.
The blocks are numbered consecutively from 0 to n (the value of n depends on
the size of the disk).

Introduction 1-5

Each Files-11 volume has an index file, which is created when the volume
is initialized. (You cannot use a disk until it has been initialized with the
INITIALIZE command.) The index file contains the following information:
• Bootstrap block
•Home block
• File headers
The bootstrap block is physically the first block on the volume. All Files--11
volumes have an area for this bootstrap block even if the operating system
does not require a bootstrap block. If the volume is not the operating system
volume, the bootstrap block area contains a different program. This program
displays a message on the system console indicating that the volume is not the
operating system volume, but is, rather, a volume containing only user files.
The home block is normally the next block on the volume; it identifies the
disk as a Files-11 volume. If for some reason the home block cannot be read
(physically unusable), an alternative block will be selected for use as the
home block. This block provides specific information about the volume and
default values for files on the volume. Among the items in the home block are
the following:
• The volume name
• Information to locate the remainder of the index file
• The maximum number of files that can be present on the volume at any one
time
• The User Identification Code (UIC) of the owner of the volume
• Volume protection information (specifies which users can read and/or write
the entire volume)
Files-11 volumes contain several copies of the home block to ensure against
accidental destruction of this information and the consequent inability to
locate other files on the volume.
The bulk of the index file consists of file headers; each file header describes
one file on the volume. File headers contains information such as the file
ownership, protection, creation date, and creation time. Most importantly,
the file header contains a list of extents that make up the file, describing
where the file is physically located on the volume. If a file has a large number
of extents, multiple file headers are used to describe them. A file identifier
number is associated with each file header.
When you create a file, you normally specify a file name to VAX-11 RMS,
which assigns this name to the file on a Files-11 volume. VAX-11 RMS places
the file name and file identifier associated with the newly created file in a
directory, which contains an entry defining the location for each file. When
you access the file, you supply the file name, which associates with the file
identifier through the directory entry. The file identifier, in turn, points to the

1-6 Introduction

location of the file header which contains a listing of the extent or extents that
locate the actual data.

1.4 Basic Tape Concepts
You can also use tape as a file storage medium with VAX-11 RMS. VAX-11
RMS supports the standard magnetic tape structure defined by American
National Standard X3.27-1977, Magnetic Tape Labels and Record Formats
for Information Interchange.
Data records are organized on magnetic tape in the order in which they
are written. In other words, the organization of data on magnetic tape is
sequential.
Characters of data on magnetic tape are measured in bits per inch (bpi). This
measurement is called density. A 1600 bpi tape can accommodate 1600 characters of data in an inch of recording space.
Even though a tape may have a density of 1600 bpi, there are not always 1600
characters on every inch of magnetic tape because of the interrecord gap
(IRG). The IRG is an interval of blank space between data records; it is
created automatically when records are written to the tape. The IRG is a
breakpoint on the tape, which allows the tape unit to decelerate, and stop if
necessary, after a record operation and then accelerate to working speed
before the next record operation.
Each IRG is approximately 0.6 inch in length. Writing an 80-character record
at 1600 bpi requires 0.05 inch of space (the IRG, therefore, requires twelve
times more space than the data). Clearly, this wastes valuable storage space.
VAX-11 RMS can reduce the size of this wasted space by using record blocking. This technique groups individual records into a block and places the IRG
after the block rather than after each record. (A difference exists between a
block on disk and a block on tape: on disk, a block is fixed at a size of 512
bytes; on tape, the size of a block is user determined.) However, record blocking requires more buffer space to be allocated for your program, thus increasing VAX-11 RMS memory requirements. The greater the number of records
in a block, the greater the buffer size requirements. You must determine the
point, based on the configuration of your computer system, at which the
benefits of record blocking cease.
The following example shows how space can be saved by record blocking. A
1600 bpi tape contains 10 records that are not grouped into a block. Each
record is 160 characters long (or 0.1 inch at 1600 bpi) with a 0.6 inch IRG after
each record. This would use 7 inches of tape. However, placing the same 10
records into one block uses only 1.6 inch of tape (1 inch for the data records
and 0.6 inch for the IRG). Figure 1-4 illustrates this example of record
blocking.
Record blocking also increases the efficiency of the flow of data into the
computer. For example, 10 unblocked records require 10 separate physical
transfers, while 10 records placed into a single block require only one physical

Introduction 1-7

transfer. Moreover, a shorter length of tape is traversed for the same amount
of data; thus the operation is completed in less time.
Figure 1-4: Interrecord Gaps
WITHOUT RECORD BLOCKING

Re~rd Rec~rd Rec~ord Record Rerrd Record Record Record Record Record

~ml·:~-\:~=;:.

~m:=_:'.,[=_·\:~.-._.:~j_:[·=·=!

J J , i~·~.:~;~_:~={·=~

m 1RG . , 1RG ~-;=t~:·:.,·~=\ _\ 1RG ~~l
.. .='.

::=:::

1
~~~~~~~

:::::~·

\~I\

I RG lM
~lM~ I RG -~:~:_1_:.\:·~::~.~:'. I RG
=~~~~~:

.::::::

~-=.'._:~.~=-.:~:·_:ti_::i::.l=·.:\

~====

:::::::

.:i_,:I.:_:~

I RG "'_ :t_
.:l_:_::1.:1"_
.

,.,.,.

I RG

*:\:_\_:.~.:_.:~:·r_:l:.~

IRG

WITH RECORD BLOCKING
Al I 10 records

IRG

Data on magnetic tape is also organized into files. When you create a file on
tape, the file system writes a set of header labels on the tape immediately
preceding the data blocks. These labels contain information such as the usersupplied file name, creation date, and expiration date. Additional labels,
called trailer labels, are also written following the file. To access a file on tape
by the file name, the file system searches the tape for the header label set that
contains the specified file name.
When the data blocks of a file, or related files, do not physically fit on one
volume (a reel of tape), the file is continued on another volume. This is a
multivolume tape file. All the volumes contained in the multivolume file
constitute a volume set. When access is made to a file on a volume set, all
volumes in the set are searched.
For additional information about tape and disk structures, see the VAX-11
Record Management Services Reference Manual.

1-8 Introduction

Chapter 2
VAX-11 RMS Files

2.1

Overview
This chapter briefly describes the following:
• VAX-11 RMS file contents
• VAX-11 RMS file organization
• VAX-11 RMS record access modes (retrieving and storing)
• VAX-11 RMS record characteristics (format)
• VAX-11 RMS file size
All functionalities described in this chapter are available at the MACRO
level. This is not always the case, however, for higher-level languages. Users of
higher-level languages should refer to the appropriate section of their language manual to see which RMS functionalities are available to them.

2.2 File Contents
AV AX-11 RMS file is a collection of logically related records treated as a unit
and arranged in a useful order. The contents of each record in the file are
defined by your program that creates the file. Any subsequent programs that
access this file must use the same definitions. For example, your program to
create records in a payroll file must contain the definition of each item of data
in the record. In that program, you divide the record into functional groups,
known as fields (which can also be divided into subfields). For a payroll
application, each record in the file might be divided into .fields such as the
following:
• Employee name
• Social security number
• Pay rate
• Deductions
The user that creates the file selects the length of each field and the number of
fields, and thus determines the length of each record. Each programmer with
access to this file determines how each record is used in a given application.

2.3 File Organization
File organization is the physical arrangement of records in the file. File organization is related to, but distinct from, the record access mode, which is the

2-1

manner in which the records in the file are stored and retrieved. The purpose
of file organization is to arrange the records in an orderly manner so that you
can access them in the quickest and most feasible way. You select the type of
file organization at file-creation time; it cannot be changed thereafter (although a utility conversion routine may be used to copy this file to another
volume, or a different area on the same volume, re-creating it with a different
type of file organization). VAX-11 RMS allows you to select from three types
of file organizations:
1.

Sequential

2. Relative
3. Indexed
The following subsections describe the fundamental structure of each of these
organizations.

2.3.1

Sequential Organization

In sequential file organization, records in a file are arranged in one-after-theother fashion. The sequential file organization is supported for all device
types; indeed, for all devices except disk, it is the only organization supported.
The sequence in which records appear is the order in which they were written
to the file. In other words, if you need to access the fourth record, it can be
found between the third and fifth records. In general, this ·would look like
Figure 2-1.

Figure 2-1: General Picture of Sequential File Organization

First
record

Second
record

___ ____

,___

___.

Third
record

Fourth
record

Fifth
record

Sixth
record

____ _______ ____

__,__ ------"..._

_...._

__.__

___.

You can only add records to a sequential file at the current end of the file.
This is because the physical location of each record is fixed in relation to all
other records in the file. Therefore, there is no unused space where a new
record might be inserted.
When you update an existing record in a sequential file (retrieving the record,
altering its contents, and reinserting the record in its original position), you
cannot change the length of the record.

2-2 VAX-11 RMS Files

2.3.2 Relative Organization
The second method of file organization, called relative file organization, is
available on disk devices only. This type of organization is more complex than
sequential organization but also more powerful. A relative file consists of a
series of fixed-length positions (or cells) that are consecutively numbered from
1 to n. This number is the relative record number; that is, the number of the
record gives its position relative to the beginning of the file. Each record
written into the file is assigned to a specific cell within the file. For example,
the second record written might be placed in the fourth cell; it would then be
relative record number 4. When searching for this record, you must direct
VAX-11 RMS to the record by specifying its relative record number. This
assignment can result in cells that do not contain records being interspersed
in the file.
Relative file organization allows random retrieval of records by means of the
relative record number. The relative record number of a record in a relative
file is the key value in random access mode; refer to Section 2.4.2 for a
detailed description of random access by key. The fixed-length cells let
VAX-11 RMS calculate the record's actual position. The unused cells accept
new records as they are inserted into the file. A record can also be deleted
from any cell in the file, thereby freeing cells for new records.
Figure 2-2 shows, in general, a relative file organization.

Figure 2-2: General Picture of Relative File Organization
Relative cells

First
record
written

Empty
cell

Second
record
written

Third
record
written

Fourth
record
written

Fifth
record
written

To access a record in a relative file by random mode, you must know the
relative record number (key) of the record. One method of keeping track of
each record's cell is to store records based on a numeric value within the
record (for example, an account number being equivalent to the relative
record number).
Although each record in a relative file is assigned to a fixed-length cell, the
actual size of the individual records can vary in length (that is, different size
records can be in the same file). Clearly, the size of each record must be less
than or equal to the size of the fixed-length cell. For example, assume that the
fixed length of each cell in a relative file is 256 bytes. Suppose only three

VAX-11 RMS Files 2-3

records are in the file, each of a different length; the first record is 192 bytes
long, the second 128 bytes, and the third 253 bytes. Each of these records can
reside in the same relative file because each occupies its own fixed-length cell,
as shown in Figure 2-3. Note that each record is prefixed by three bytes that
indicate the record length and whether this cell is empty (a delete flag). These
bytes are used only by V AX-11 RMS; you need not be concerned with them,
except when planning the file's space requirements.
Figure 2-3: Variable-Length Records in Fixed-Length Cells
FIXED-LENGTH CELLS

256 bytes

----------...

256 bytes

--~~--./'----~~-- ------~-- --~~----~~--""---~~--,
Record 1
192 bytes used

Record 2
128 bytes used

__::::~·3: _J

Legend:
.

= VAX-11 RMS control information bytes

•Unused bytes

2.3.3 Indexed Organization
The third method of file organization, called indexed file organization, is
available on disk devices only. This type of organization allows you to store
records in predefined sort orders. The keys of the file define the sort orders.
You can then retrieve these records sequentially by one of the sorted orders or
randomly by one of the record's sort values. Because V AX-11 RMS completely controls the placement of records in an indexed file, the location of
records is transparent to your program.
A key (a character string, a packed decimal number, a 2- or 4-byte unsigned
binary number, or a 2- or 4-byte signed integer) is defined by its location and
length within each record. When identifying the location and length of character string keys, you can define single or segmented keys. A simple key is a
single contiguous string of characters in the record. A segmented key, however, can consist of from two to eight such strings; these strings do not need to
be contiguous. When processing records that contain segmented keys,
VAX-11 RMS treats the separate segments as a logically contiguous string.
Integer, binary, and packed decimal keys are always simple keys.
At least one key, or sort order, must be defined for an indexed file. This
mandatory key is the primary key. Optionally, additional keys may be defined, which are referred to as alternate keys. Each alternate key is also
defined by its location and length within the record. Your program uses the
contents of an alternate key in a record to identify that record in the alternate

2-4 VAX-11 RMS Files

sort order. As your program inserts records into an indexed file, VAX-11 RMS
uses the values of the primary and alternate keys to build indexes. An index is
the structure that allows the sorted records to be retrieved randomly.
In addition to defining simple or segmented keys, you can specify key characteristics. Those key characteristics are as follows:
1. Duplicate key (primary and alternate) values are allowed

2. Key (alternate only) values can change
3. Key (alternate only) values can be null values
When you specify that duplicate key values are allowed, you indicate that
more than one record in an indexed file can have the same value for that key.
Such records, therefore, have the same record identifier. Only the first record
with a duplicate key value can be retrieved randomly; subsequent records
must be retrieved sequentially. This capability is applicable only to indexed
files. In relative files, the record identifier, representing a relative record number, is always unique.
When you specify that key values can change, you indicate that records can
be updated with a modified value in the key; however, this characteristic is
limited to alternate keys. When such modification occurs, VAX-11 RMS automatically updates the appropriate index to reflect the new key value.
The third key characteristic that you can specify, the null key value, indicates
that when the record is put into the file, the key value may be a null value;
however, this characteristic is limited to alternate keys. VAX-11 RMS does
not make an entry in the index for this record. If the record is subsequently
updated with a key value, VAX-11 RMS then makes an entry in the appropriate alternate index.
You can also declare the converse of these characteristics. That is, you can
specify that for a given key, duplicate key values are not allowed, key values
cannot change, and there is no null value. When duplicate key values are not
allowed, VAX-11 RMS rejects any request to put a record into the file when
that record contains a key value that is already present in another record.
Similarly, when key values cannot change, VAX-11 RMS does not allow your
program to update a record by modifying the key value. Records whose keys
cannot be null values always have an entry in the appropriate alternate index.
VAX-11 RMS builds and maintains a separate index for each key that is
defined for the file. Each index is stored in the file. Thus, an indexed file
contains at least one index, for the primary key, and when alternate keys are
defined, the file contains another index for each alternate key.
Figure 2-4 illustrates the general structure of an indexed file which has only
the primary key defined, the primary key being the names of employees in an
employment record file. Figure 2-5 illustrates the general structure of an
indexed file which has the primary key and one alternate key defined, the
primary key being the names of employees and the alternate key being the
badge number of employees in an employment record file.

VAX-11 RMS Files 2-5

N
I

<
>
~
I

........
........

r:n

KEY DEFINITION

BAKER

..i.-~~~~~~~~~~~~~~~-t~~~~

ADAMS

ADAMS I PINE ST

35112

BAKER

CLARK

I ELM AVE

WYMAN

PRIMARYINDEX(EmployeeNamel ~~~~~~~~+-~~~~~~~~~~~-....

CLARK

24379

SMITH

JONES

MAIN ST

19724

TAYLOR

SMITH

I HOLT RD I

WYMAN

11733

I
I
WYMAN I MAIN ST I
I
I

2254

'-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~- DATARECORDs~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~---

Note: Assumes one record per bucket.

Figure 2-4: Single-Key Indexed File Organization

PRIMARY INDEX

ALTERNATE INDEX

(Employee Name)

(Badge Numbe<)

4551

21000

---

-~_.L.~-------------

>------

/_t

----

<
>

x
I

~
~

I MAIN ST I 19724
I
I

::0
~

I HOLT ROI

11733

2254

'-~~~~~~~~~~~~~~~~~~~~~~~OATARECORDS~~~~~~~~~~~~~~~~~~~~~~~--'

Note: Assumes one record per bucket.

N
I

WYMAN I MAIN ST I

Figure 2-5: Multiple-Key Indexed File Organization

Each data record is placed in the file in sorted order by primary key. In
alternate indexes, the sort sequence is established by key ordering pointers to
the actual record. These mechanisms enable the records to be read sequentially in sorted order by any key.

2.4 Record Access Modes
Record access mode is the manner in which the records in a file are stored and
retrieved. This is different from file organization, which is the physical
arrangement of records in the file.
VAX-11 RMS provides three types of record access modes:
1. Sequential

2. Random by key
3. Random by record's file address (RFA)
While you cannot change the file organization once it is established (at filecreation time), the record access mode can change each time the file is used.
In fact, the record access mode can even change for each record access to a
file. This means, for example, that a relative file can be processed in sequential record access mode one time and in random by key (relative record number) record access mode the next time. Table 2-1 lists the combinations of
record access modes and file organizations permitted by VAX-11 RMS.

Table 2-1: Record Access Modes and File Organizations

Record
Access Mode
Permitted

File Organization

Sequential

Relative

Indexed

Sequential

Yes

Yes
- · - - ·· - - 1

Random
by Key

No 1

Yes 3

Yes
- - - ·------1

Random by
Record's .File
Address

Yes 2

Yes

Random access by relative record number for sequential files is permitted for fixedlength record format on disk devices.

Random access by record's file address is permitted only on disk devices.

The key for relative files is the relative record number.

2-8 VAX-11 RMS Files

The following subsections describe the record access modes and the capability
for switching record access modes during program execution.

2.4.1

Sequential Access

In sequential access, record storage or retrieval starts at a designated point in
the file and continues in one-after-the-other fashion through the file. When
using the sequential record access mode, a program issues a series of requests
to VAX-11 RMS to retrieve or store the next record in the file. VAX-11 RMS
interprets these requests in the context of the organization of the file. As
shown in Table 2-1, the sequential access mode is available for all types of file
organization: sequential, relative, and indexed. The subsections that follow
describe how sequential access deals with each type of file organization.
2.4.1.1 Sequential Access to Sequential Files - In a sequential file, records
are virtually adjacent to each other. To read a particular record within the file
using sequential access mode, your program must open the file (initiate file
processing) and successively read the records preceding this record. Each
record can be retrieved only by first retrieving all the records that physically
precede it.

Figure 2-6 shows a surface of a disk volume. Each lettered section on the
surface represents a record in a sequential file, beginning with record A. When
your program issues a series of requests to access the records sequentially,
VAX-11 RMS interprets these instructions in the context of the file organization. Since this particular file is sequential, VAX-11 RMS knows that every
record after the first record follows the current record; thus, it implicitly
knows the position for the next record access.
Figure 2-6: Sequential Access to a Sequential File

User Program

VAX-11 RMS

Read
next record
Read
next record
Read
next record

-------

Sequential access does not allow you to backspace to a record that was already
passed. You have to restart at the first record by either reopening the file or
rewinding the file, or by using dynamic access (see Section 2.4.4). In addition,
you can add records only to the end of the file.
2.4.1.2 Sequential Access to Relative Files - Relative files also permit sequential access (see Table 2-1). This holds true even if not all the fixed-lengtH
cells in the file contain records. Empty cells, representing records that were

VAX-11 RMS Files 2-9

never written (or records that were deleted), can occur in a relative file.
VAX-11 RMS recognizes whether successive record cells in a relative file are
empty or contain records; VAX-11 RMS ignores the empty cells and searches,
in succession, for cells that contain records. For example, a relative file might
contain records only in cells 1, 3, and 6. Successive sequential read requests
cause VAX-11 RMS to read the record in cell 1, then cell 3, and then cell 6.
Figure 2-7 shows how VAX-11 RMS checks each cell, ignores an empty cell
when it finds one, and then checks the next cell for a record.
Figure 2-7: Sequential Read of a Relative File
VAX -11 RMS

User Program
Read
next record
Read
next record

--Re.....
ad--L-+------..-- -- next record

.._+------i - - - - -

When using sequential access to write :records to a relative file, VAX-11 RMS
places the new record in the empty cell whose relative number is one higher
than that used for the previous write (or read) request. New records cannot be
written into cells that already contain records. As Figure 2-8 shows, your
program directs VAX-11 RMS to write record Finto cell 2. Record A already
occupies cell l, but cell 2 is empty, so VAX-11 RMS can write the record into
this cell. If this request were followed by a request to write the next record,
VAX-11 RMS would write into cell 3 which is also empty. If you attempt to
write into a cell already occupied by a record - for example, by issuing yet
another request to write the next record - the attempt will fail. You can,
however, request VAX-11 RMS to update (change) an existing record.
Figure 2-8: Write to a Relative File
User Program

VAX-11
RMS

Cel I 1, start
of file

Write record
F to cell 2
/

/
/
Cell 2,
now contains _ _____,...
record F

2-10 VAX-11 RMS Files

Sequential Access to Indexed Files - In an indexed file, VAX-11
RMS uses one or more indexes to determine the order in which to process
records in sequential access mode. The entries in an index are arranged in
ascending order by key values. Thus, an index represents a logical ordering of
the records in the file. If you define more than one key for the file, each index
associated with a key will represent a different logical ordering of the records
in the file. Your program, then, can use the sequential access mode to retrieve
records in the order represented by any index.

2.4.1.3

When reading records from an indexed file in sequential mode, your program
must initially specify to V AX-11 RMS a key of reference (for example, primary key, first alternate key, second alternate key, and so on). Thereafter,
V AX-11 RMS uses the index associated with that key of reference to retrieve
records in the same sequence as the entries in the index. Each successive
record that VAX-11 RMS returns in response to your program's read request
contains a value in the specified key field that is equal to (when duplicate
keys are allowed) or greater than that of the previous record returned.

In contrast to a sequential read request, a sequential write request to an
indexed file does not require a key of reference. Rather, VAX-11 RMS uses
the stored definition of the primary key to place the record in the file and the
definition of alternate keys to place entries for the record in the alternate
indexes. When your program issues a series of sequential write requests,
V AX-11 RMS verifies that each successive record contains a key value in the
primary key field that is equal to or greater than that of the preceding record.

2.4.2 Random Access by Key
In random access by key, your program, not the file organization, determines
the order in which record processing occurs. Each program request for a record
must include the key value (relative record number for relative files and key of
reference plus the key value for indexed files) of the particular record to be
accessed.
Random access is always supported for relative and indexed files. V AX-11
RMS also permits random access by relative record number for sequential
disk files, but only if the records in the file are of fixed length (see Sections
2.4.3 and 2.5.1.1).
Unlike sequential access, which always follows the one-record-after-the-other
access order, random access follows no specific, predefined pattern. Your program randomly identifies, by means of the key value (relative record number
for relative files and key of reference plus the key value for indexed files), any
record within the file and VAX-11 RMS retrieves (or writes) that record. Your
program may make successive requests for accessing or retrieving records that
are anywhere within the file. For example, as shown in Figure 2-9, your
program directs VAX-11 RMS to read the sixth record of a relative file. The
circled numbers indicate the order of access requests; in this case the sixth
record is C. The program then directs V AX-11 RMS to read the second record
(record F).

VAX-11 RMS Files 2-11

Figure 2-9: Random Access by Relative Record Number (Key)
Start of file

User Program

VAX-11
RMS

1. Read sixth
record

2. Read second
record

Compare this figure with those for sequential access (Figures 2-6 and 2-7).
Each of your program's read requests in random access mode to an indexed
file must specify a key value and the index (for example, primary index, first
alternate key index, second alternate key index, and so on) that VAX-11
RMS must search. When VAX-11 RMS finds, by means of the index, the
record that matches the key value, it reads the record and passes it to your
program. Random access can be accomplished on any key by any of the
following methods:
• Exact match of key values.
• Approximate match of key values (that is, record key value greater than
your program-supplied key value, or record key value greater than or equal
to your program-supplied key value).
• Generic match of key values. Generic match is applicable to string data
type keys only. A generic match is defined as a match on some number of
leading characters in the key. You determine the number by specifying a
search key smaller than the entire field.
• Combination of approximate and generic match.
In contrast to read requests, which require your program-specified key value,
your program requests to write records randomly in an indexed file do not
require the separate specification of a key value. All keys (primary and, if any,
alternate key values) are in the record itself. When an indexed file is opened,
VAX-11 RMS retrieves all key definitions stored in the file. Thus, VAX-11
RMS knows the location and length of each key field in a record. After writing
a record into the file, VAX-11 RMS examines the key values in the record,
and creates new entries in the appropriate alternate indexes.
In this way, VAX-11 RMS ensures that the record can be retrieved by any of
its key values.

2.4.3 Random Access by Record's File Address
Every record in a file has a unique address within the file - the record's file
address (RF A). This is another mode of retrieving records in all types of file

2-12 VAX-11 RMS Files

organizations, as long as the file resides on a disk. RF A mode provides the
only means of randomly accessing a sequential file with variable-length records.
An important feature of RF A is that the address remains constant as long as
the record exists in the file. VAX-11 RMS returns the RFA to you in a
parameter block when the record is read or written. You can either ignore the
RF A or retain it to use as a pointer to the record whenever you need to access
the record.
Figure 2-10 contains two illustrations. The first shows that when you write a
record in a file, its RFA is returned to you. The second illustration shows that
when this record is needed for a subsequent operation, and you supply the
RFA, VAX-11 RMS simply uses the RFA to find the record directly.

Figure 2-10: Random Access by Record's File Address

User Program

VAX-11

RMS
Write record
B

Record's file
address

User Program

VAX-11

RMS
Read record
by RFA

Record's file
address

VAX-11 RMS Files 2-13

2.4.4 Record Access Mode Switching
VAX-11 RMS lets you switch from one type ofrecord access mode to another
while processing a file. This is known as dynamic access. Dynamic access is
not a record access mode in itself; rather, it is a term that describes the
capability of changing record access modes in mid-stream. No limitation exists on the number of times such switching can occur. The type of file organization must support the types of record access modes selected (see Section
2.4.2 for the restrictions on random access by relative record number with
sequential files).
Dynamic access can be most effective immediately following a random-access
operation. When a program randomly accesses a record, VAX-11 RMS establishes a current record position in the file for the program. If the program
switches dynamically to sequential access, VAX-11 RMS interprets this
switch to sequential access as a request for the next record (or records, if
desired). Then, using the randomly accessed record as the starting point of the
file, VAX-11 RMS can obtain subsequent successive records in the file using
the sequential access mode.
For example, in the sequential file shown in Figure 2-11, the records were
written in account-number order, and each account number has more than
one record (for every transaction, the user created one record).

Figure 2-11: Sequential Account File for Dynamic Access

First record in account C ~

I s Is I

_c~_c I_~] c___.___c_J
..,,,...,,..,,.. .....

/
,,..,,..,,..,,..

..,,,... .....

,,.....,,,...

,,..,,....,,,...,,..,,....,,,...

Suppose the need arises for a list of all transactions in account C. As described
above, the normal manner of processing a sequential file is to sequentially
access each record in the file. However, if the user has saved the RFA returned
in the parameter block when the first record in account C was created, then
random access by RF A can be used to establish a starting point at the first
record in account C, rather than at the beginning of the file. Then, with
dynamic access, the user can switch to sequential access to retrieve
the remaining records, as shown in Figure 2-12.

2-14 VAX-11 RMS Files

Figure 2-12: Using Dynamic Access to Switch Record Access Modes
User Program
VAX-11

Read first record in
account C by RF A,
switch access mode to
sequential, read
remaining C records.

RMS

.....

~,
\

''~

The program logic must allow the program to identify the point in the file at
which sequential access is no longer needed. The program can then direct
VAX-11 RMS as to what step to follow, such as switching back to random
access to select other records. It is also possible to use sequential access,
switch to random access, and return to sequential access, if desired. This is
very useful when you want to return to a record that was already passed in the
sequential record access mode.

2.5 Record Characteristics
VAX-11 RMS provides the mechanism for programs to process files. Certain
characteristics of these files are apparent to the user. These characteristics
are:
• The record formats
• The storage structure (buckets and areas)
The following subsections describe record formats and storage structure.
2.5.1

Record Formats

VAX-11 RMS is not concerned with the actual contents of records, except for
the values contained in key fields of records within indexed files. It deals
instead with the record format, which is the way a record physically appears
on the recording surface of the storage medium.
VAX-11 RMS provides a choice of three different record formats:
1. Fixed length
2. Variable length
3. Variable with fixed-length control (not supported for indexed files)
These record formats are supported for sequential, relative, and indexed file
organizations, except as noted. In relative files, all records are stored in fixed-

VAX-11 RMS Files 2-15

length cells, even though the records themselves might be of variable-length
or variable with fixed-length control format.
The term fixed-length record format refers to
a file whose records are all of the same size. In a fixed-length record file, the
number of bytes of data per record is set to a given number at file-creation
time. Each record, then, occupies an identical amount of space in the file;
however, not all of a record's data bytes need contain information. Unused
bytes can exist in each fixed-length record. If so, you are responsible for
recognizing any unused fields.
2.5.1.1 Fixed-Length Records -

You specify the size of the fixed-length records when you create the file. This
size specification becomes part of the information that VAX-11 RMS stores
and maintains for the file; it cannot be changed.
The term variable-length record format
refers to a file whose records need not be of the same size. Because the number
of bytes of data per record is not fixed, each variable-length record occupies
only as much space as it needs to contain the data of that record.
2.5.1.2 Variable-Length Records -

To allow retrieval of variable-length records from a file, VAX-11 RMS prefixes a count field to each record when it writes the record to the file. VAX-11
RMS constructs this count field from information that you provide in your
program, and considers the count field separate from the record data.
VAX-11 RMS uses two types of variable-length formats: V format and D
format. The format used depends on the device on which the file resides:
1. Disk files -

V format

For variable-length records in files residing on disk volumes, VAX-11
RMS writes a 2-byte (1-word) binary count field before the data field of
each record. This number does not include the count field itself.
2. Tape files -

D format

To comply with the American National Standard X3.27-1977, when using
magnetic tape volumes, VAX-11 RMS writes a 4-byte decimal count field
before the data field of each record. In contrast to V-format records, this
number does include the count field. Before VAX-11 RMS returns the
count to you, it adjusts the count so that the value returned always
reflects the length of your data.
When creating variable-length records, you can specify the size of the largest
record permitted in the file. Any attempt to write a record larger than this size
results in an error. If you specify a value of 0, any length record can be written
in the file; note, however, that for relative and indexed files, a record must be
entirely contained within a bucket.
2.5.1.3 Record Formats and File Organizations - The following paragraphs
describe the effects of the various file organizations under the fixed-length
record and variable-length record formats.

2-16 VAX-11 RMS Files

Figure 2-13 compares the fixed- and variable-length record formats described
above, as they apply to sequential files. Each format shows a portion of a file
that contains three records. The comparable record in each format contains
the same number of bytes. The first record has 8 bytes, the second 16, and the
third 24. For the fixed-length record format, the record length was set at 32
bytes. Therefore, VAX-11 RMS considers ·an 32 bytes to be used, when, in
fact, unused bytes may exist as far as the user is concerned. This figure shows
how much storage space the variable-length record can save. On the other
hand, if records are to be updated in place, the original size of the record
cannot be changed. Thus, for some applications, providing some "wasted"
space achieves a certain amount of flexibility.

Figure 2-13: Comparison of Fixed- and Variable-Length Records

Fixed
length

24
bytes

bytes

\.....__

___ ----

-----~-----------------

32 bytes*

D format
variable
length
(tape)

I
I

II bytes

24
bytes

bytes

I
I

four byte
count fields

V format
variable
length
(disk)

24
bytes

two byte
count fields

*VAX-11 RMS considers all 32 bytes to be used, even though they may not contain useful information in the eyes of the user.

VAX-11 RMS Files 2-17

In the relative file organization, all records, both variable length and fixed
length, are written into fixed-length cells. Therefore, variable-length records
do not save space in the relative file organization. In fact, two additional bytes
per record are required to store the record size.
In the indexed file, variable-length records are truly variable. Their lengths
are limited only by the size of the data bucket or by a user-defined maximum
record size. Since record size can change on update, you need not write variable-length records at their maximum size.
2.5.1.4 Variable with Fixed-Length Control Records - Variable with fixedlength control records are similar to variable-length records. 1 However, variable with fixed-length control records include a fixed-length control field in
addition to the variable-length data portion. At file-creation time, you specify
two sizes. The first specification indicates the size of the largest record permitted in the file. Any record larger than this size results in an error (unless
you specify 0). The second specification is the size of the fixed control area,
which precedes every record in the file. You specify the size of the fixed
control area once, and that size is fixed for every record in the file.

A fixed control area allows you to construct records that contain additional
data that may have no direct relationship to the other contents of the record.
For example, the fixed control area may contain line-sequence numbers for
every record in the file. The sequence numbers would not be used in any
program operations involving the record, but you would probably find them
useful in locating the record on a search operation, such as in an edit of the
file.
Before writing a variable with fixed-length control record to a file, you construct the record in two separate locations: the fixed control area and the data
portion. When writing the record to the file, VAX-11 RMS fetches both the
fixed control area and the data portion from their respective locations and
joins both portions to form the record (placing the fixed control area before
the data portion). VAX-11 RMS uses the record size information that you
provide to determine the length of the data portion only. This joined record is
then prefixed by a count field that describes the total length of the record.
Figure 2-14 shows the path VAX-11 RMS takes to write a variable with fixedlength control record to a file.
When reading a variable with fixed-length control record, VAX-11 RMS uses
the count field to determine the combined length of the fixed control area
portion and the data portion. Then VAX-11 RMS separates the fixed control
area from the data portion of the record for processing, as shown in Figure
2-15. VAX-11 RMS subtracts the fixed length of the fixed control area portion from the record count; thus returning to your program the length of the
data portion only. You can ignore the fixed control area portion of a record
simply by not specifying a separate buffer for the fixed control area.

This record format is not applicable to indexed files.

2-18 VAX-11 RMS Files

Figure 2-14: Writing a Variable with Fixed-Length Control Record

Fixed control area
portion
Create record
(user action)

VAX-11
RMS
Data portion

Write record
and prefix
count field

1 - - - - - - . i Count

field

Fixed control area
portion

Data portion

Variable with
fixed-length control record

Figure 2-15: Reading a Variable with Fixed-Length Control Record

Read record
(user action)

VAX-11
RMS

Count
field

Separate record

Fixed control area
portion

Data portion

Process data
(user action)

Data portion

Fixed control area
portion

VAX-11 RMS Files 2-19

2.5.2 Storage Structure
VAX-11 RMS uses a logical storage structure called a bucket for building and
processing relative and indexed files. A bucket contains from 1 to 32 blocks.
You specify the number of blocks in a bucket when you create the file.
Unlike a block, however, a bucket cannot contain a portion of a record;
VAX-11 RMS never permits records to span bucket boundaries. When specifying the size of a bucket, you must consider the maximum size of any record
that can be written into the file, record overhead, and bucket overhead, as
well as the number of records that will fit in the bucket. Since buckets are
units of transfer, large buckets help provide good disk throughput for sequential operations, but require more buffer space in programs that process them.
Indexed files can be segregated into areas. Areas are portions of a file that are
treated independently in terms of initial allocation, extensions, and bucket
sizes. Areas enable the data records and each index of a file to be separate
units. This allows the bucket sizes to be customized according to the sizes of
the data records and keys. It also allows localization of the various parts of an
indexed file.

2.6 File Size
The size of a file is expressed as a number of blocks. Each block within a file is
a unit of data whose size depends on the physical medium on which the file
resides. For example, blocks for files on disk devices are each 512 bytes. This
size is established by the disk device itself and cannot be altered. On magnetic tape, a block is the information between two interrecord gaps. This size
varies between 18 and 65,535 bytes, and is established by you, the user. The
interrecord gaps separate the end of one block from the start of another (see
Section 1.4).
When you create a disk file, as explained in Section 1.3, you can specify how
many blocks are to be initially allocated to the file, in the range of 1 to
4,294,967 ,295. These blocks can be allocated over multiple volumes of a related volume set. VAX-11 RMS allocates the required number of blocks, and
stores their retrieval information in the file header. Block numbers in a file
always start at 1, and continue to the total number of blocks in the file. If you
do not specify the number of blocks to be allocated, VAX-11 RMS, by default, allocates blocks depending on the space it calculates is needed for the
file. This uses disk space very efficiently, because only a very small amount of
space is wasted by allocating more space than necessary.
However, if you eventually need more space for the file, VAX-11 RMS must
perform another allocation, a moderately time-consuming operation. (You can
also specify how many additional blocks for VAX-11 RMS to automatically
allocate if the file must be extended.) Furthermore, if VAX-11 RMS performs
a large number of relatively small extensions to a file, the relocation information necessary to retrieve the blocks increases, thus adversely affecting retrieval performance. For large or frequently extended files, you can achieve
considerable processing efficiency by specifying, to VAX-11 RMS, appropriate initial and default extension quantities.

2-20 VAX-11 RMS Files

This numbering scheme for blocks, called virtual block numbering, makes a
file seem like a series of adjacent blocks. In terms of physical layout, however,
blocks are not always adjacent, even though they are numbered consecutively.
For example, blocks 10 and 11 are adjacent in terms of the virtual block
numbering scheme, but may not be physically adjacent. One or more other
blocks belonging to other files could be placed between them.
The virtually numbered blocks of a file on disk consist of groups of blocks
called extents. Within an extent, consecutively numbered blocks occupy consecutive physical locations. However, a file can be segmented into several
different areas on disk if not enough contiguous area is available to contain
the whole file, or if different extents were allocated at different times. The
blocks in each extent are contiguous, but each extent is not contiguous to the
other extents in the same file. For example, blocks 1 through 5 may be in one
extent, and blocks 6 through 10 may be in another.
When a file consists of only one extent, the file is contiguous, since all consecutively numbered blocks of the file correspond to consecutive physical locations. When creating a file, you can request that VAX-11 RMS allocate the
file contiguously. One advantage of contiguous files on devices accessed by a
single user is that disk access arm movement is minimal compared to noncontiguous files; therefore, access is faster.
The blocks of a file contain the records written into the file. Depending on the
size of the records, a block can contain one record, more than one record, or
only part of a record. When a particular record is larger than the size of a
block, the record is stored in as many consecutively numbered blocks as
necessary to contain the entire record. In this instance, the record is said to
cross or span block boundaries. Total file size will vary, of course, based upon
whether the records of a file are allowed to cross block boundaries.
On magnetic tapes, consecutively numbered blocks actually occupy consecutive physical locations. Blocks from one file are never interspersed with blocks
from another.

VAX-11 RMS Files 2-21

Chapter 3
File and Record Processing

3.1

Processing Levels
A program processes VAX-11 RMS files at two different levels: the file level
and the record level.
At the file processing level, VAX-11 RMS and the operating system provide
operations that act on the file as a whole. They also provide an environment
that controls access to the file by other users and permits more than one
program to access, or share, a given file at the same time, as shown in Figure
3-1.

Figure 3-1: Shared File Access

Program 1

Program 2

Program 3

VAX-11 RMS determines the types of permissible sharing from information
contained in the accessing programs.
At the record level, programs perform operations on individual records. Record operations can be performed either synchronously or asynchronously.
That is, VAX-11 RMS allows your program to choose between receiving program control only after VAX-11 RMS completely satisfies a record operation
request (synchronous), or possibly receiving control after VAX-11 RMS has
initiated the request but before it has been completely satisfied (asynchronous). Asynchronous operations thus allow the program to overlap processing
and I/0 operations. This is in contrast with file-level operations, such as
opening a file, which are always synchronous.

3-1

For both synchronous and asynchronous record operations, VAX-11 RMS
provides two record transfer modes: move and locate. In move mode, VAX-11
RMS copies a record from an I/0 buffer into a buffer which you have specified. For input operations, data is first read into the I/0 buffer from a peripheral device (such as a disk), and then moved to your user buffer for processing.
For output operations, you first build the record in your buffer; VAX-11 RMS
then moves the record to an I/0 buffer. When an entire block is filled in the
1/0 buffer, the block is written to the peripheral device.
In locate mode, VAX-11 RMS addresses records directly in an 1/0 buffer.
Usually, this reduces program overhead because records can be processed
directly within the I/0 buffer. Locate mode is available only for input operations.
Other VAX-11 RMS facilities allow programs to control 1/0 buffer space
allocation or simply leave all space management to VAX-11 RMS.
The following subsections briefly describe the file-level and record-level processing environments, and the different modes of file access that a program
can use with VAX-11 RMS.

3.2 The File Level Operations
VAX-11 RMS provides seven operations at the file level:
• Create
Creates a new VAX-11 RMS file of any organization. You must create a file
before VAX-11 RMS can process it.
•Open
Initiates the file processing for an existing VAX-11 RMS file. You must
open a file before its records can be accessed.
• Display
Returns the attributes of a VAX-11 RMS file to your program. Among the
attributes are such items as protection information, record format and size,
and file allocation information.
• Extend
Increases the allocated size of an existing VAX-11 RMS disk file. You use
this operation when you want to explicitly control file-space allocation.
• Modify
Alters certain file attributes of an existing VAX-11 RMS disk file. Such
alterations include changing the file to a noncontiguous file and changing
the limit on the maximum number of records
• Close
Terminates VAX-11 RMS file processing. Once a file is closed by a program, it cannot be accessed by the same program unless it is reopened.

3-2 File and Record Processing

• Erase
Deletes a VAX-11 RMS disk file and makes its space available for use by
another file. Erasing a file also removes its entry from the directory file.

3.2.1

File Protection

VAX-11 RMS allows you to assign a protection specification to a file at the
time the file is created. This determines the file access rights of users and
potential users of the file by assigning them membership in one of the following classes:

• System
This class specifies the access rights for users that the system manager
designates as privileged users.
• Owner
This class specifies the access rights of the owner of the file. The owner is
the particular member of a group to which the file belongs.
• Group
This class specifies the access rights granted to users that the system manager designates as members of the same group as the owner of the file.
•World
This class specifies the access rights of any user. Normally, a user with
world privileges is one who is not a member of the system, owner, or group
class.
Within each of the above classes, there are four separate access right specifications, representing the different types of access granted to the users in that
class. These access right specifications provide for read, write, execute, and
delete operations.

3.2.2 File Sharing
Timely access to files r~quires that more than one concurrently active program be allowed to simultaneously process the same file. Through its filesharing capability, VAX-11 RMS permits several programs to access a file at
the same time. File sharing depends on:
• Device and file organization
Because tape units are limited to sequential operations, magnetic tape files
cannot be shared. Disk files, however, can be shared by multiple processes.
Unrestricted sharing by any combination of readers and writers of relative
and indexed files is permitted. In addition, sharing is allowed for sequential
files with 512 byte fixed-length records. Sharing of other types of sequential
files, however, is permitted only with restrictions.

File and Record Processing 3-3

• Explicit file-sharing information specified by the accessing programs
Although the organization of a file determines whether multiple readers and
writers can access the file, your program provides the information that
allows the actual sharing. You control the degree of sharing of the file by an
explicit sharing specification that you give to VAX-11 RMS when you create or open the file. The sharing specification indicates which types of
operations can be used by the sharing users.
When your program opens a file, it must provide two types of information.
First, it must state what type of operations it intends to perform, such as
read, write, or update. The intended operations are then checked against
the protection for the file. Second, the program must specify which types of
operations other concurrently active programs can perform on the file. The
combination of these two types of information allows VAX-11 RMS to
determine which programs can gain access to the file. When the sharing
specification of one program is compatible with the sharing specification of
another program, both programs can gain access to the file simultaneously.
File sharing is supported only for native-mode programs using VAX-11
RMS. Programs (tasks) that run in compatibility mode using the RSX-11
Applications Migration Executive and RMS-11, cannot share files with
native mode programs using VAX-11 RMS or with other programs running
in compatibility mode and using RMS-11.

3.3 The Record Level Operations
VAX-11 RMS provides five major operations at the record level:
• Get (Read)
Reads (retrieves) a record from a file
• Put (Write)
Writes (inserts) a record into a file
•Find
Locates a record in a file
• Update
Alters the contents of a record that currently exists in a file
• Delete
Removes an existing record from a file
See the VAX-11 Record Management Services Reference Manual for other
record-level operations.
3.3.1

Synchronous and Asynchronous Modes of Operation

Your program can handle record operations on a file in either of two ways:
synchronously or asynchronously. When operating synchronously, the pro-

3-4 File and Record Processing

gram issuing the record operation request regains control only when the request is completely satisfied. Most high-level languages support synchronous
operation only. In asynchronous operations, the program can regain control
before the request is completely satisfied.
For instance, when synchronously reading a record from a file, the program
regains control only after the record is passed to the program. In other words,
the program is in a wait state until the record returns; no other processing (for
this program) takes place during this read-and-return cycle. On the other
hand, when asynchronously reading a record, the program might be able to
regain control before the record is passed to the program. The program can
thus use the time normally required for the record transfer between the file
and memory to perform some other computations. However, another record
operation cannot be started on the same stream (an access-window to a file,
associated with a record access control block supporting record operation
requests) until the prior record operation is complete. Record operations on
other streams can be initiated.
Whether the program will actually regain control before the record operation
is complete depends on several factors. For example, the required record may
already reside in the 1/0 buffer (see Section 3.3.2); or the operating system
may schedule another program, thus possibly allowing a necessary 1/0 operation to be completed before the original program is rescheduled.
One factor to consider in the use of asynchronous record operations is that you
must include a separate completion routine or V AX-11 RMS wait request in
the issuing program. This routine is required to determine when the record
operation is complete, since the next record operation for that stream cannot
be initiated until the prior operation is completed.

3.3.2 Record Buffering
VAX-11 RMS uses internal memory areas called I/O buffers to read or write
blocks of data. To your program, record processing under V AX-11 RMS appears as the movement of records directly between a file and the program
itself. This is, in fact, not the case. Transparently to your program, VAX-11
RMS reads or writes blocks or buckets of a file into or from an I/O buffer.
Records within the buffer are then made available to the program.

The transfer of data between a file and the I/O buffers depends on the file's
organization. For the sequential organization, VAX-11 RMS reads and writes
a block or series of blocks. For relative and indexed organizations, V AX-11
RMS reads and writes buckets.

3.3.3 Record Transfer Modes
In addition to specifying synchronous or asynchronous record operations, your
program can use either of two record transfer modes to gain access to each
record in memory. These modes are move mode and locate mode.
V AX-11 RMS permits move mode record operations for all file organizations.
Move mode requires that an individual record be copied between the 1/0

File and Record Processing 3-5

buffer and your program buffer. For read operations, VAX-11 RMS transfers
a block (or series of blocks or a bucket, depending on the file organization and
size of the 1/0 buffer) into an 1/0 buffer, finds the desired record within the
buffer, and then moves the record to a program-specified location (a user
buffer). For a write or update operation, your program must first build or
modify the record in a program-defined work area. When you issue a write
request, VAX-11 RMS moves the record to the 1/0 buffer that VAX-11 RMS
will use for writing to the file.
In contrast to move mode, in locate mode the data records stay in place;
VAX-11 RMS need not copy records from an I/0 buffer to a user buffer. A
pointer is set up to allow your program to access the records directly. This
reduces the amount of data movement, thereby saving processing time. This
mode is actually a partial locate mode because VAX-11 RMS cannot always
avoid moving data records as, for example, when records cross block boundaries. Because of this, a user buffer is still required.

3.3.4 Record Locking
VAX-11 RMS can lock records to control operations to a relative or indexed
file that more than one record stream within a process, or more than one
process, can access simultaneously. This record-locking facility ensures that a
program can add, delete, or modify a record on one stream without the program's needing to check that the same record is not simultaneously accessed
by another stream or process. For example, when your program opens a file
with the declared intention of writing or updating records on multiple
streams, VAX-11 RMS locks the record accessed by the program. This locking prevents another stream or process from accessing the same record until
the first stream or process releases the record.
VAX-11 RMS also handles the automatic locking of the entire bucket that
contains the record for the short period required to initially access the record.
This automatic lock also occurs later, when the actual update takes place. In
the interim, the record remains locked, but other records in the bucket can be
accessed and modified as required.
There are facilities you can use to allow VAX-11 RMS to handle automatic
record locking and unlocking; facilities also exist that give you explicit control
over the release of record locks.
VAX-11 RMS does not provide record locking support for sequential files with
other than 512 byte fixed-length records. However, the user can provide the
necessary synchronization logic to allow simultaneous reading and writing of
those files.

3.4 Creating the File
You can use several methods to create a VAX-11 RMS file. The most common
is to issue a $CREATE macro instruction (or its equivalent in a high-level
language) within an application program. At creation time, you specify the
file definition information, which VAX-11 RMS stores within the file for
reference in later processing. A second method is to use the VAX-11 RMS
DEFINE utility program.
3-6 File and Record Processing

Note that neither of the above creation procedures actually stores records in
the file; this must be done by your application program or by the VAX-11
RMS CONVERT or Indexed File Load utility programs.

3.5 Processing Records in a File
The organization of a file determines the types of operations that a program can perform on records. VAX-11 RMS can perform the following major
operations:
• Read a record your program.

VAX-11 RMS returns an existing record within the file to

• Write a record -

VAX-11 RMS adds a new record to the file.

• Find a record - VAX-11 RMS locates an existing record in the file. It does
not return the record to your program, but establishes a new current position in the file (see Section 2.4.4).
• Delete a record -

VAX-11 RMS removes an existing record from a file.

• Update a record - Your program modifies the contents of a record that has
been read from the file into a buffer area. VAX-11 RMS writes the modified
record into the file, replacing the old record.
Table 3-1 shows the combinations of major record operations and file organizations that VAX-11 RMS permits, and notes the exceptions to these operations. Table 3-1: Record Operations and File Organizations

Record
Operation
Permitted

File Organization

Sequential

Relative

Indexed

Read (Get)

Yes

Write (Put)

Yes 1

Yes

Find

Yes

Delete

Yes

Update 3

Yes 2

Yes

In a sequential file, VAX· 11 RMS allows records to be added at the end of the file
only. (Records can be written to other points in the file through an update operation.)

When performing an update operation to a sequential file, the user cannot change
the length of the record.

VAX-11 RMS allows update operations on disk devices only.

File and Record Processing 3-7

3.5.1

Processing Sequential Files

In a sequential file, a program can read existing records from the file using the
sequential record access mode. If the file resides on disk, the random by RFA
record access mode can also be used (see Section 2.4); and, if the file is of
the fixed-length record format, the random by relative record number record
access mode is permitted. You can add records only at the end of the file.

All record access modes (sequential, random by relative record number, and
random by RF A), allow you to establish a new current position for a record in
the file (find operation). In the sequential record access mode, you can skip
records with a find operation. In either the random by relative record number
or the random by RF A record access mode, a find operation can establish a
random starting point in the file for sequential read operations.
The sequential file organization does not allow the deletion of records from the
file since this organization requires that records be adjacent to each other.
However, you can update an existing record in a sequential file as long as:
1. The record resides in a file on a disk
2. The modification of the record does not alter its size

3.5.2 Processing Relative Files
The relative file organization permits greater program flexibility in performing record operations than the sequential organization. A program can read
existing records from the file using sequential, random by key (relative record
number), or random by RFA record access modes. You can write new records
either sequentially or randomly, as long as the intended record position (cell)
does not already contain a record.
All record access modes for relative files allow you to position to a record in
the file (find operation). After finding the record, VAX-11 RMS permits you
to delete the record from the relative file. After record deletion, the empty cell
is available to a new record. In addition, your program can update records
anywhere in the file. If the records are variable length, the update operation
can modify the record length up to the maximum size specified when the file
was created.

3.5.3 Processing Indexed Files
The indexed file organization provides the greatest flexibility in performing
record operations. A program can read existing records from the file in sequential, random by RFA, or random by key access mode. When reading records in
random by key access mode, the program specifies one of four types of
matches:
1. Exact key match
2.

Approximate key match

3. Generic key match
4.

Approximate and generic key match

3-8 File and Record Processing

Exact key match requires that the key value in the retrieved record precisely
match the key value specified by the program read operation.
Approximate key match allows the program to select either one of the following relationships between the key value of the retrieved record and the key
value specified by the program:
1. Equal to or greater than

2. Greater than
The advantage of this kind of match is that if the requested key value does not
exist in any record of the file, VAX-11 RMS returns the record that contains
the next higher key value. This allows the program to retrieve records without
knowing an exact key value.
Generic key match means that the program need specify only an initial portion of the key value. VAX-11 RMS then returns to the program the first
occurrence of a record whose key value begins with these characters. This
capability is useful in applications in which a series of records must be retrieved when only the initial portions of their key values are identical.
The final type of key match combines both the generic and approximate
facilities. The program specifies only an initial portion of the key value, as
with generic match. In addition, the program specifies that the key value of
the retrieved record must be either one of the following:
1. Equal to or greater than the program-supplied value

2. Greater than the program-supplied value
VAX-11 RMS also allows you to write any number of new records into an
indexed file. It rejects a write operation only if a key value in a record violates
a user-defined key characteristic, such as duplicate key values not allowed.
You can perform a find operation, similar to the read operation, in sequential,
random by RF A, or random by key access mode. When finding records in
random by key value access mode, the program can specify any one of the four
types of key matches provided for read operations.

In addition to reading, writing, and finding a record, your program can delete
or update any record in an indexed file. During an update operation, the
modification cannot violate user-defined key characteristics; for ex.ample, if
key values cannot change, the update is rejected when that condition is
detected.

3.6 Block Input/Output
Block input/output (I/0) lets programs bypass the VAX-11 RMS record processing capabilities entirely. Thus, rather than perform record operations by
means of the supported record access modes, you can process a file as a logical
structure consisting solely of a number of blocks.
Block I/O operations provide you with an intermediate step between VAX-11
RMS operations and coding directly at the explicit 1/0 instruction level of the

File and Record Processing 3-9

system services. Using block I/O allows you full control of the data of the
individual blocks of a file while also enabling you to take advantages of the
VAX-11 RMS capabilities for opening, closing and extending a file.
In block 1/0, a program reads or writes one or more blocks by specifying a
starting virtual block number in the file and the length of the transfer. Regardless of the organization of the file, VAX-11 RMS accesses the identified
block or blocks for you.

Because VAX-11 RMS files contain internal information meaningful only to
VAX-11 RMS itself, DIGITAL does not recommend that you modify an existing file using block I/0 if the file is also to be accessed by VAX-11 RMS
record-level operations. (Block I/O does not update the internal record information correctly.) The block 1/0 facility, however, does allow you to create
your own file organizations. This file structure must be maintained through
specialized user-written programs and procedures; VAX-11 RMS cannot
access these structures through its record access modes.

3-10 File and Record Processing

Glossary

alternate key

An optional key within the data records in an indexed file; used by VAX-11 RMS to
build an alternate index. See key (indexed files) and primary key.
area

Areas are VAX-11 RMS maintained regions of an indexed file. They allow a user to
specify placement and/or specific bucket sizes for particular portions of a file. An area
consists of any number of buckets, and there may be from 1 to 255 areas in a file.
asynchronous record operation

An operation in which your program may possibly regain control before the completion of a record retrieval or storage request. Completion ASTs and the $WAIT
MACRO are the mechanisms provided by RMS for programs to synchronize with
asynchronous record operations. See synchronous record operation.
bits per inch

The recording density of a magnetic tape. Indicates how many characters can fit on
one inch of the recording surface. See density.
block

A group of consecutive bytes of data treated as a unit by the storage medium. A block
on a Files-11 disk structure is 512 eight-bit bytes.
block 1/0

The set of VAX-11 RMS procedures that allow you direct access to the blocks of a file
regardless of file organization.
bootstrap block

A block in the index file of a system disk. Can contain a program that loads the
operating system into memory.
bpi

See bits per inch.

Glossary-1

bucket

A storage structure, consisting of from 1 to 32 blocks, used for building and processing
relative and indexed files. A bucket contains one or more records or record cells.
Buckets are the unit of contiguous transfer between VAX-11 RMS buffers and the
disk.
buffer

An internal memory area used for temporary storage of data records during input or
output operations.
cluster

The basic unit of space allocation on a Files-11 disk volume. Consists of one or more
contiguous blocks, with the number being specified when the volume is initialized.
compatibility mode

A mode of execution that enables the central processor to execute nonprivileged
PDP-11 instructions. The operating system supports compatibility mode execution
by providing an RSX-llM programming environment for an RSX-llM task image.
The operating system compatibility mode procedures intercept calls to the RSX-llM
executive and convert them to the appropriate operating system functions.
contiguous area

A group of physically adjacent blocks.
cylinder

The tracks at the same radius on all recording surfaces of a disk.
density

The number of bits per inch of magnetic tape. Typical values are 800 bpi and 1600
bpi. See bits per inch.
directory

A file used to locate files on a volume. A directory file contains a list of files and their
unique internal identifications.
dynamic access

Term applied to the switching from one type of record access mode to another while
processing a file.
extent

One or more adjacent clusters allocated to a file or a portion of a file.

2-Glossary

file

An organized collection of related items (records) maintained in an accessible storage
area, such as disk or tape.
file header

A block in the index file describing a file on a Files-11 disk structure, including the
location of the file's extents. There is at least one file header for every file on the disk.
file organization

The physical arrangement of data in the file. You select the specific organization
from those offered by VAX-11 RMS, based on your individual needs for efficient data
storage and retrieval. See indexed file organization, relative file organization, and
sequential file organization.
files-11

The standard physical disk structure used by VAX-11 RMS.
fixed control area

An area, prefixed to a variable-length record, containing additional information that
can be processed separately and that may have no direct relationship to the other
contents of the record. For example, the fixed control area might contain line
sequence numbers for use in search operations.
fixed-length record format

Property of a file in which all records are of the same size. This format provides
simplicity in determining the exact location of a record in the file and eliminates the
need to prefix a record size field to each record.
home block

A block in the index file, normally next to the bootstrap block, that identifies the
block as a Files-11 volume and provides specific information about the volume, such
as volume label and protection.
index

The structure which allows retrieval of records in an indexed file by key value. See
key (indexed files).
index file

A file on each Files-11 volume that provides the means for identification and initial
access to the volume. Contains the access data for all files (including itself) on the
volume: bootstrap block, home block, file headers.

Glossary-3

indexed file organization

A file organization which allows random retrieval of records by key values and sequential retrieval of records in sorted order by key value. See key (indexed files).
interrecord gap

An interval of blank space between data records on the recording surface of a magnetic tape. Allows the tape unit to decelerate, and stop if necessary, after a record
operation and then accelerate before the next record operation.
IRG

See interrecord gap.
key

Indexed files: a character string, a packed decimal number, a 2- or 4-byte unsigned
binary number, or a 2- or 4-byte signed integer within each data record in an indexed
file. You define the length and location within the records; VAX-11 RMS uses the
key to build an index. See primary key, alternate key, and random access by key
value.
Relative files: The relative record number of each data record in a data file; VAX-11
RMS uses the relative record numbers to identify and access data records in a
relative file in random access mode. See relative record number.
locate mode

Technique used for a record input operation in which the data records are not copied
from the 1/0 buffer. See move mode.
move mode

Technique used for a record transfer in which the data records are copied between the
I/O buffer and your program buffer for calculations or operations on the record. See
locate mode.
multiple-extent file

A disk file having two or more extents.
native mode

The processor's primary execution mode in which the programmed instructions are
interpreted as byte-aligned, variable-length instructions that operate on the following
data types: byte, word, longword, and quadword integers; floating and double floating character strings; packed decimals; and variable-length bit fields. The other
instruction execution mode is compatibility mode.

4-Glossary

primary key

The mandatory key within the data records of an indexed file; used by VAX-11 RMS
to determine the placement of records within the file and to build the primary index.
See key (indexed files) and alternate key.
random access by key

Indexed files only: Retrieval of a data record in an indexed file by either a primary or
alternate key within the data record. See key (indexed files).
Relative files only: Retrieval of a data record in a relative file by the relative record
number of the record. See key (relative files).
random access by record's file address

Retrieval of a record by the record's unique address, which VAX-11 RMS returns to
you. This record access mode is the only means of randomly accessing a sequential
file containing variable-length records.
random access by relative record number

Retrieval of a record by its relative record number. See relative record number. For
relative files, random access by relative record number is synonymous with random
access by key. See random access by key (relative files only).
record

A set of related data that your program treats as a unit.
record access mode

The manner in which VAX-11 RMS retrieves or stores records in a file. Available
record access modes are determined by the file organization and specified by your
program.
record blocking

The technique of grouping multiple records into a single block. On magnetic tape an
IRG is placed after the block rather than after each record. This technique reduces
the number of I/0 transfers required to read or write the data; and, in addition (for
magnetic tape), increases the amount of usable storage area. Record blocking also
applies to disk files.
record format

The way a record physically appears on the recording surface of the storage medium.
The record format defines the method for determining record length.
record length

The size of a record; that is, the number of bytes in a record.

Glossary-5

record locking

A facility that prevents access to a record by more than one record stream or process
until the initiating record stream or process releases the record.
record cell

A fixed-length area in a relative file that can contain a record. The concept of fixedlength record cells lets VAX-11 RMS directly calculate the record's actual position in
the file.
record's file address

The unique address of a record in a file, which is returned by RMS whenever a record
is accessed, allows records in disk files to be accessed randomly regardless of file
organization. This address is valid only for the life of the file. If an indexed file is
reorganized, then the RFA of each record will typically change.
relative file organization

The arrangement of records in a file where each record occupies a cell of equal length
within a bucket. Each cell is assigned a successive number, called a relative record
number, which represents the cell's position relative to the beginning of the file.
relative record number

An identification number used to specify the position of a record cell relative to the
beginning of the file; used as the key during random access by key mode to relative
files.
reorganization

A record by record copy of an indexed file to another indexed file with the same key
attributes as the input file.

RFA
See record's file address.
RMS-11

A set of routines which are linked with compatibility mode programs, and provide
similar functional capabilities to VAX-11 RMS. The file organizations and record
formats used by RMS-11 are identical to those of VAX-11 RMS.
sequential file organization

The arrangement of records in a file in one-after-the-other fashion. Records appear in
the order in which they were written.

6-Glossary

sequential record access mode

Record storage or retrieval which starts at a designated point in the file and continues
in one-after-the-other fashion through the file. That is, records are accessed in the
order in which they physically appear in the file.
synchronous record operation

An operation in which your program does not regain control until after the completion of a record retrieval or storage request. See asynchronous record operation.
stream

An access window to a file associated with a record access control block, supporting
record operation requests.
track

A collection of blocks at a single radius on one recording surface of a disk.
variable-length record format

Property of a file in which records need not be of the same size.
variable with fixed-length control record format

Property of a file in which records of variable-length contain an additional fixed
control area capable of storing data that may have no bearing on the other contents of
the record. Variable with fixed-length control record format is not applicable to
indexed files.
VAX-11 Record Management Services (VAX-11 RMS)

The file and record access subsystem of the VAX/VMS operating system for the
VAX-11. VAX-11 RMS helps your application program process records within files,
thereby allowing interaction between your application program and its data.
volume

Disk: An ordered set of 512-byte blocks. The basic medium that carries a Files-11
structure.
Magnetic tape: A reel of magnetic tape, which may contain a part of a file, a complete file, or more than one file.
volume set

A collection of related volumes.

Glossary-7

Index
A
Access modes,
defined, 2-8
dynamic, 2-13
file organization and, 2-1
random to indexed files, 2-11
random to relative files, 2-11
random to sequential files, 2-11
random access by record file address, 2-12
sequential to indexed files, 2-11
sequential to relative files, 2-9
sequential to sequential files, 2-9
switching, 2-13
Advantages of card files, 1-1
Advantages of disk, 1-1
Advantages of magnetic tape, 1-1
Alternate key,
defined, 2-4
duplicates, 2-5
indexed files, 2-5
used in sequential access to indexed
files, 2-11
Asynchronous record operations, 3-1

B
Bits per inch, 1-7
Block, 1-2, 2-19
Block 1/0, 3-9
Block size of disk files, 2-19
Block size of tape files, 2-19
Blocks, 2-19
numbering scheme of, 2-20
Bootstrap block, 1-6
Bucket, 2-19
Bucket boundaries,
defined, 2-19
locking of, 3-6
Buffers, 3-5

c
Card files,
defined, 1-1
advantages of, 1-1
disadvantages of, 1-1
Cells,
contents, 2-3
defined, 2-3

Cells, (Cont.)
empty, 2-3, 2-9
numbering of, 2-3
relative record number, 2-3
role in sequential access, 2-9
writing new records in, 2-10
Cluster, 1-3
Concepts of disk, 1-2
Concepts of magnetic tape, 1-7
Creation of VAX-11 RMS files, 3-6
Cylinder, 1-4

D
Data field, 2-1
Data format, 2-1
Definition of file organization, 2-1
Definition of record format, 2-15
Definition of relative organization, 2-2
Definition of sequential organization, 2-2
Definition of VAX-11 RMS, 1-2
Delete operations, 3-4, 3-7
Density, 1-7
Disadvantages of card files, 1-1
Disadvantages of magnetic tape, 1-1
Disk extents, 1-3, 2-20
Disk files, 2-20
block size of, 2-20
Disk,
advantages of, 1-1
concepts of, 1-2
defined, 1-1
Dynamic access, 2-14
effective use of, 2-14
program logic for, 2-15

E
Effective use of dynamic access, 2-14
Extents,
defined, 1-3

F
File,
contents, 2-1
header, 1-6
processing level, 3-1

Index-I

File, (Cont.)
protection, 3-3
record characteristics, 2-15
sharing, 3-3
sharing guidelines, 3-3
size, 2-20
storage media in general, 1-1
storage space, 1-4
File Control Services-11, 2-15
File organization,
combinations of access modes and, 2-8
combinations of record formats and, 2-16
combinations of record operations and, 3-7
definition, 2-1
indexed, 2-4
purpose of, 2-1
relative, 2-2
selection of, 2-1
sequential, 2-2
types of, 2-2
Files-11,
block, 1-4
bootstrap block, 1-6
cluster, 1-3
cylinder, 1-4
disks, 1-2
extent, 1-3
file headers, 1-6
file name, 1-6
hierarchy, 1-4
home block, 1-6
identifier, 1-7
index file, 1-6
INITIALIZE command, 1-6
record, 1-5
track, 1-4
VAX-11 RMS disk files, 1-2
volume, 1-4
volume set, 1-4
Fixed control area, 2-18
Fixed-length records, 2-16

H
Header labels, 1-8
Home block, 1-6

I
Index,
alternate key, 2-4
ascending order of, 2-11

Index-2

Index, (Cont.)
building of, 2-4, 2-5
creating new entries in, 2-4
defined, 2-4
entries in, 2-4
primary key, 2-4
Indexed File Processing, 3-8
Indexed files,
bucket locking of, 3-6
random access to, 2-5, 2-11
record operations, 3-8
sequential access to, 2-5, 2-11
storage medium, 2-4
Indexed organization,
defined, 2-4
Interrecord gap, 1-7, 2-20

K
Key,
alternate, 2-4
character string, 2-4
defined, 2-4
duplicates allowed, 2-5
duplicates not allowed, 2-5
primary, 2-4
segmented, 2-4
simple, 2-4
Key values,
approximate, 2-12
approximate and generic, 2-12
exact, 2-12
generic, 2-12
random access by, 2-12

L
Limitations of record access mode
switching, 2-13
Locate mode record transfer, 3-5

M
Magnetic tape, 1-1
advantages of, 1-1
concepts of, 1-8
disadvantages of, 1-1
Move mode record transfer, 3-5
Multivolume file, 1-8

N
Numbering scheme of blocks, 2-20

p
Primary key,
defined, 2-4
duplicates allowed, 2-5
index building, 2-4
used in sequential access to indexed
files, 2-11
Processing levels,
file, 3-1
record, 3-1
Processing of VAX-11 RMS files, 3-7
Processing operations for VAX-11 RMS
files, ;~-6
Program logic for dynamic access, 2-14
Purpose of file organization, 2-1
Purpose of relative organization, 2-3

R
Random access,
defined. 2-11
search pattern of, 2-11
Random access by key value, 2-11
Random access by record's file address, 2-12
Random access by relative record number,
2-11
Reading a variable with a fixed-length control
record, 2-18
Reason for fixed control area, 2-18
Reason for record's file address, 2-13
Record access mode,
types of, 2-8
Record access mode switching,
defined, 2-14
limitations of, 2-14
Record,
access mode, types of, 2-8
access mode switching, 2-14
blocking, 1-7
cells, 2-2, 2-16
characteristics, 2-15
contents, 2-1
defined, 1-5
format types, 2-15
keys in, 2-4
locking, 3-6
processing level, 3-1
size, 1-5
transfer modes, 3-5
Record's file address,
defined, 2-12
random access by, 2--13
reason for, 2-13

Record format,
defined, 2-15
Record-length count field, 2-16
Record level operations,
delete, 3-4, 3-7
find, 3-4, 3-6
get (read), 3-4, 3-6
put (write), 3-4, 3-6
update, 3-4, 3-7
Relative file organization,
defined, 2-2
purpose of, 2-3
Relative file processing, 3-8
Relative files, 2-2
sequential access to, 2-9
Relative record number, 2-2
random access by, 2-11

s
Search pattern of random access, 2-11
Segmented keys, 2-4
Selection of file organization, 2-1
Sequential access to relative files, 2-9
Sequential access to sequential files, 2-9
Sequential file organization,
defined, 2-2
record addition to, 2-2
sequential access to, 2-9
update to, 2-2
Sequential file processing, 3-8
Sequential files, 2-2, 2-9
sequential access to, 2-9
Sequential record access mode, 2-9
Simple key, 2-4
Storage structure, 2-20
Synchronous record operations, 3-1, 3-2

T
Tape files, 2-20
block size of, 2-20
Track, 1-4
Trailer labels, 1-8
Types of file organization, 2-1, 2-2
Types of record access mode, 2-8

v
Variable with fixed-length control records,
defined, 2-18
reading, 2-18
writing, 2-18

Index-3

Variable length records, 2-16
VAX-11 RMS, 1-2
VAX-11 RMS files, 3-6
VAX/VMS operating system, 1-2
Volume protection, 1-6
Volume set, 1-4

Index-4

w
Writing a variable with fixed-length control
record, 2-18

Introduction to VAX-11
Record Management Services
AA-D024C-TE

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