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AC-S866A-M0

April 1987

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Document:	CHQFSA0 XXDP+ File Struct Doc Apr81
Order Number:	AC-S866A-M0
Revision:	0
Pages:	18
Original Filename:	http://bitsavers.org/pdf/dec/pdp11/xxdp/AC-S866A-M0_CHQFSA0_XXDP+_File_Struct_Doc_Apr81.pdf

OCR Text

B 1

SEQ 0001
1DEN Tl FIe ATI ON

T NAME:

AC-s866A-MO

PROf;·U( T NAME:

CHQF SAO XXDP+ FILE STRuC T DOC

PRODUCl DATt:

APRIL 1981

MAINTAINER!

DIAGNOSTIC SYSTEM") ENG1NEERING

fhe ir.formation in this document is sucje, ~ to changE' wnnout notice

J and SnolJ~d not ~e. constru-:d as it tOfMlit1't'W?nt by Digital Equipment
t orp()rat len. 0191 tat EqulpmEHlt. Corpqrat ion aSS\.Ifles no respons; bi t i ty
i
any err'ors that may appear In Hl'Is document.
j

I No responsibi lit,. is assumed for the USe or ret iabH it)' of software on

i
t

pment tha~ is not supplied by Digital or its attil iated companies.

f {;;Jpyriaht
((}:
. ..
._
~

,1981 bY- Dirt}
tal Equi pment Corporat i I)n
;:J
~

lfotlo,w1ng at~. trad~mar~sof D.igital EQuipmeht Corporation:
J

tat. PDP .. UN1SU5

MASSaUS; DEC, DECUS. DECtape~ DEC/Xll

It
t

II
If

\
\

C 1

DOCUMENT: \(XFORM.MEM
DATE:

17 FEB 1981

CHARGE NUMBER: P98-08823

XXDP+ fILE STRUCTURE
SPECi F1CAT Io,"l
REV1~IQN

MAINTAINED BY:

0.0

D1AGNOSTlC

SYSTEM

FNGINEERING

REVISlON HlSTORY
REVlSION 0.0
by

FEB 17 1981

Michael Cinnamon

SEQ 0002

D 1

Page

INl'ROOUCT ION

2.G
2.1

i)ATA STRUCTURES
OATASLOCKS

2
2

, 2 .. 1 ~ 1

RANDOM ACCESS DEVICES

SEQUENTIAL ACCESS DEVICES

FlLE STRUCTURES

TYPES OF FILES

3.1" 1

CONTIGUOUS FILES

3.1.2

TEXT FllES

• ()

3 .. 0

1.2.3 BINARY FILES

MEDIA STRUCTURE

L. 1,

RANDOM ACCESS STRUCTURE

4.1.1

MASTER FILE DlRECTORY

4.1.2

USER FlU: DIRECTORV

4. 1.:3

a1T MAP

4. L4kAND~ ACCtSSDEV1CE INf'~RMAt10N

4.2

SEQUENtIAL ACCESS DEvICE

4.2.1

MAG1APE

4.;: .. 2 CASSETTe
GLOSSARY

SEQ 0003

E 1

Page 2
i.Q

I NT RODUC. nON

The structure that XXDP+ uses for storing files on media is unique to
The structure was origilially based on DOS-11 but it has since
tJE'en modi fled to accommodate the needs 0 f XX{)P+.. a l though many

:o:OP,,_

similarities still exist.

XXDP+ ~upports both random access and sequential access type devices.
A directory index structure is used for accessing files on random
access type devices such as disks.
For sequential devices like
magtape
a header record containing file information precedes each
#

fHe.

I 2.0

DATA STRUCTURES

Ie.

Data Bloc ks

I
! "1

I The basH unit of data transferred in XXDP+ file IIO ;s a data block.
I A data

block is defined as a group of 512(10) 8 bit bytes.

12.1.1 Random Access Devices.
1
1Ot:\ random access de,{ices" data blOcks are addressed by their logi~al
I bu:;)(k ntlnber.. log1cal blocks are data blocks that are addressable ln
f . t in~'\r ordered faShion.
The order ranges from 0 to n-1, where n is
i the rRaxim'-'l\nll'nher of blocks supported on the device. The variable n
vaf'ies depending on the device but is not greater than 65535 (10).
This
I me an $. that no matter how many data blocks phySically reside on a device only
. the first n blocks are acce~sible.

logical blocks are not necessarily the same as phySical blo::ks.
A
phySical block is usually limited to the amount of data a physical sector
cMtains which may be ~ess than 512 (10)

i houses at most one loglCal block.

bytes.

Also a

physical block

r A I. inked list of logical blocks is set up using linked blccks.
,~
itl~~d
block is a logical block that devotes the first word of the
bloc k to contain a link word. The pnk word. cO'!t ains the log; cal bLoc k
f1l~er of another block.
A tero l1nk word lndlcatfls that tne block
containir19 it is the last block of the l. ist.

SEQ 0004

F 1

Page 3

. ;>. ' • '2

SequEmt) al Ac cess Devi ces

s&Quf.mtial access devices such as magtape and cassette, data blocks
stored as 512 byte records.
Because XXDP+ uses the same
r@cad/write routines for both random and sequential access devices.
ogical linked blocks arE! stored on ~equentiaL type devicE's.

\)'1
I

are

the link word is only some non-zero vaLue to indicate that
are more blocks in the list. A zero link word indicates the
last block of the list.

I-towi"vt.l>f.

there

'3.0

FILE STRUCTURES

5~1

Types Of Files

ar. tnree types of files supported by xxuP+.
They are contiguous
files, text files a~d binary files. This is not to mean that other types
of fHes cannot be stored on an XXDP+ medium. but XXDP+ only has the
capabH it)' to produce these types.
rh~re

3"l.1

Contiguous Fit@!

~\ contiguous
1~iately
'i~iatety

fH.: h: a set of logical blocks which

physically reside
media.
The term
adj;.. cfnt ;$ obvious for sequential devices but not
quite &s appa' e.nt for random access devices. For these it means for
any logical bl'Jc1I. f'\. the ne~t contiguous block is located at n+·'.
19UQUS

adjacentt

one~

another

the

fHElI's ere normaUy used to store core image

><Xf)P+ mon i tor.

data

such

rex t f 1
)It files arfrlO "hl,de up of a set :~'"
of t inked blocks.
Each block
or,taki'$ 510(10) 8 bft ASCIi harQ-ters. At: ASCll nuLl character (a
bytf' with a vat.ue ot l'ero) is used to :"idicate the end of the file.

SE (.I 0005

G 1

Page 4
3.1.~

Binary Fil~s

Bina"y fH'l's are use~ to stor~ executab.le pr:ograms. ,They ar:e made up
of a ser,es of l1hked blocks each of WhlCh cnntaln sectlons of the
program. These sections are in absolute formatted binary and there ;s
; at Teast one per logical block.
lh~

absOlute formatted binary specification is ~s follows:

- Contains a value of 1 to indicate startinq point.
- Contains a vaLue of O.
BvTES 3: af"\d 4 - Contains number of bytes

includes bytes 1.
byte.

This must foLlow byte 1.
(N)

in this llinary block.

2, 3 and 4 but excludes the checksum

levTEs 5 and 6 - Contains

where

the starting memory address
following data bytes are to be stored.

! BYTES ., tc N

Data bytes.

j ByTE N+l

Contains thf.l\ checksLnl byte_ The checksLlTl;s the 2's
complement of the sum of the data in alL n bytes. It
is generated ignoring ovp.rflow and carry conditions.

{
I

N <= 509. The maximum number of data bytes lS

503.

the

! The ehd of a binary file is indicated uy a bit"lary block that has a
! t1t~e count qf 6. Bytes 5 and 6 contai n the program's t ran:; fer address.

I Hns bl.Qck 19 known as the transfer block
i
l A binary block with a byte count of 5 indicates a 'bias block'.
t

Bits

i (1 ·and 1 of byte 5 represent bits 16 ?nd 17# respectively; of the load
t address for the next binary block.

14.0 MEDIA STRUCTURE
14 .. 1
!

Random Access Structure

!I Atp1 eces
t XXf.>P+ random access devices are set up to contain the fal Lowing
9 1 information: . boo~strap,. monitor core image. master fi Le
I dl r@ctorH1IS (MFD), user flle d1 rec ton es (UFD). and b it maps.

I The bootstrap is a program that always occupies Logical block 0 on the
device.

c(lf'Miand

is a core

SAVM t •

image that is placed there by :he utility
The boots trap knows where on the d i sl<. the mon itor

ore i.mage res i ,;t;.>S.

image is a contiguous fHe that is 16 blocks long.
His placed on the disk by the ut;L ity command 'SAVM'. Its position
d~pends on the type of disk.
The MrD is a table of informc)t-;on which
The monil:or core

(Jt)talf1·:) pcdnters to the U~Ds and the bit maps.

SEt) 0006

H 1
Page 5
4.1.1

Master File Directory

The MfO is placed on the disk by the ~Jtil ity 'ZERO' command.
The type
f disk determines which Qf two varieties of MFD is used and where it is on
tf!@ aE'vice.

+--.----------------------+
,
LINK TO MFD2

WORD OFFSET INTO BLOCK

! ............~- ..,......--.......... ------..----.. -~ .. -- :

INTERLEAVE FACTOR
~
.
BIT MAP START BLOCK II :

f 'Ii!Ii!jIJ,. . . . . . . -,.; . . . . . . ~ ......... _""""': . . . ._wt; . . . _ _. . . . . . . _

,
I

...... . , _

!~-~-~~~~-~~~~~~~~-~~--~~~!

P01NT~R

10 81T MAP #1

POlt-HER TO 81 T MAP 112 !

...

f ........ """_,....,~ ...... _........ , . .................... _ _ .,,.,.'._ .. 1

,
:

. . . . . . . . . ..,_,~_-..._ • .__ .... _ _ _ _ ....... _ _ . . . . _.;w;o, _ _ ;

__________ ~ ___________ l
,I _ _ _PO.INTER
fO S n MAP liN .

~
:

N+2

,
'lIR.-. . .~:~~ •...., __• .-

... _ _ _ ~. . . _

•

...., . .,_ _ _ ,. . __ ~_-..

rJ+3

255

N+t. to

UNUSED

rhe interleave tattor is used as part of the block allocation
4il90rithtn.
Normatly blocks are allocated contiguously if possible
t>ut Ofi: certain d@vic,es .. th, amount of time ! ~ takes to access a t inked
l!1t of blO(KS i's r$dlJced by pLat: ing each block of the l1St a constant
number of blocks apart.
This constant n'.lT\ber is the interleave
factor.
Trye p,?inters in the table are the logical block numbers of
t h~' res.p&c t 1 II., b 1 t maps.
WORD O~FSET INTO BLOCK
!' __..... __...,.._...,.......... _o
...._.......... __
~

!;'

_,---_~_,_._

!
401
!
. . _ _ _ ............... _ .... 'M'..,...' ...................... _ _ _ _ :
. _ l ..... _ , . . . . . . . . . . . . __ . . .

'"'~

pOINTER 10 flRST ' T,.••0 BLOCK
!
...
.... _ ............ l
i
9 (10)
!

A! ... --. .......... _

.... _

. . . . . . . . . _~._..". . .._,.,..",

:-~~~-~~~-~.-~--~--~~~~~~~~-~.~~~~

!, ......__ ...._...._....... __
;
UNUSED
t

illiillt . . . . .·_,'. . _ _ . . . . . . . ~ . . . . . . . . . _

ttl•. t

iIK~rd

..........

.!
I

5-255

rst word i.s a l ink of zero indicating no more MFDs.

The second

.,orresponds to the DOS-11 UIC EL 1J. The third is the logical
ock number of the first UFD block. The fourth is the number of

dotds in each UFD entry; this is always nine

(9),

I 1
Page 6

+....,....... '4IiIa_--. _____

... __ ... __-_ .... _, ... ___ ..... _ .. __ +

WORD QFFSET INTO BLOCK

.
!

! II Of UfO 8LOCKS
! .... - ...,... -'-~.... ------.... ,..,'..------------...-- ~

! ....--........... - .........,--.--'......------------... _----- !
! It OF 8lT MAP BLOCKS
'

POINTER TO fIRST BIT MAP BLOCK!

3
4

!~~~~~-~~~-~~--~~~~----~~~~--~--~!

: POINTER TO FIRST UFD BLOCK
f ....... __

·
~

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

... _,...

... ____ .... _ ... _______ I

~~.~

! ........'_" .. _.... --...,.... ~... - ...- ...---.... ---........ --...--- !
!1 ........
POINTER
TO MFO 1/2
'...... _ .........___ .... ___ .... ______ ........ _______ ... f
·
.
!
0
!

!! __
NUMBER
Of.-..........
SUPPORTED BLOCKS
...............'..........

~ II OF BLOCKS PREALLOCATED
I
! --...,...--..'...........--......_,...,- _... - ...--......--------- !
~ INTERLEAVE
tACTOR
!
t ,• ..,.....,..
. . ._._._ ..."-__
.......,_ ........... _ ....... __ ,_ ... ____ .... _ I

!-.~--~~~~-~~~-~~~~--~~~~-~----~--~
4Il10- . . . . _

..... ___ . . _ _ _ _ _ _ _ _ _ _

! ........,....""""'.................,..-..--..-.~------..--....- ...... --..... --!
! POINTER TO FIRST BLOCK OF
I

!1 ___MONITOR
IMAGE
___,__...... _ .._CORE
............ ___
-.._..___ ........ __ ....... __ ...... _ ..... _ t

·!

10
11

! TRACK + SECTOR ADDRESS FOF BAD !

__ ____ t

_______

SECTOR FILE (SINGLE DENSITY

l~_~~~_~.~~_~~_~~~_~~_~_~

I _ ....'__ ...... _ ......._ ..--.-.,., ..... ____.... ______

! CYLINDER ADDRESS fOR BAD
I
!J' ......seCTOR
f1LE
(SlNGLE
DENSITY)
, _ , . . _ ...,_ _
..........--. ____
.... .... _ _ _
_ _ _ ..... _ _ ..._ _ _ .
•

! TRACK + SECTOR ADDRESS FOR BAD !

!f ... _SECTOR
FILE .......(DOUBLE
DENSlTY
..... _, __ ............
__........___ ....
_ ..... _______ 1
I
_~

! CYLINDER ADDRESS FOR BAD
! SECTOR FILE ([)OllJ1LE DENSITY
+--,_.......--.-----_._-----_.... _-....------_ ......--- +

ihe entry at offset 8 means the number of blocks on the device
..Jset"ved for device structure information. The last 4 entries in the
ebl. refer to the location on the disk of the DEC srD 144 bad sector
i ~ e.

SEQ 0008

J 1
Page 7
4. 1 .2
~

U,er File Directory

Gser File Directory (UFD) is a list of the files on the r ~dia.
It
(l'eatt:'d by the util it)' 'ZERO' command.
The UFD is arranged as a

inked 'i~t of logical blocks and the nLlT\ber of blocks that the UFD
,:tJ{,lies depends on the device. Each block of the UFD (('ntains space

28(10) file entries.

+----------------~--------+
______
_____
_ _ ~ BLOCK
_ _ _ _ _ _ ~1
!i _LINK
,0_ _ _NEXT
UFD

.I
:t __fILE
ENTRY
III
....... _ .... __
-__________________
·
.
t
; F1LE tNTRY 112
·I
.
i

t __ ~________ ~ ___ ~ _________

·
.
·~-------------------------j.
~ fILE ENiRY 1128(10)
~-------------------------~

4th

tile entry is a table of 9(10) words that contains the

tor'mat ion about the f i te.

+--..,........,...-... ... - .....,..---...~ .................--...... -- +

WORD

FILE NAME
t

FILE __EXTENSION
_____ ... __ ..... ____ ... I

__ I

___ ~ _____________ ~ ____ 1

,.,_...-"..,_~.,~

_ _ _ _ _ _ _ .... _ ...... _ 1

1 _, __ ..... ____ ..... "'__

1_~

,~~

!{ ...........,__
FILE
......... DATE
... _ ... ___

:
·
:

,_~

____

ACT-11 LOGICAL END
FIRST BLOCK

.!
.

!
.
______ !

1 ______ - - - - - - - - - - - - - ______ 1

fILE LENGTH

l ____ ~ ___ ~ ________ ~~

•

LAS T BLOCK

...--_ _ _ _ _ _ _ '. . . _ _ .... _

K 1
Page 8
following

1
.... _ _ _ . . .'..... , . . _ _ _ . . . . . .

ACT·11 LOG1CAl 52

+--~-------~-------~-~~--+

words, 1. 2 and 3 - The
~.~ tE~ns ion
encoded

file's
RAD-50.

six

chf=tracter

filename and 3 character

A deteted file is indicated by a zero

these three wurds.
Wt)1"d .;
W\7;f'tJ ') arid

word b
7
f

iN,(,lr d

- The DOS-11 format for the date given the file
it was put on the media.
9

ACT-11 use only.

when

Not used in X)(j)P~.

- The block number of the
file occupi~s.

first

togicaL

block that

the

The number of logical blocks that the fHe occupies.
- The block number of the last
occupies.

logical bLock that tnt 1i te

Sf 0 ({liO

Page 9

Map

(".1.~Bit

bit map is a file that contains
s*<JPQ()rted logical block on the med ia •

ThE'

the

current

status

every

. the bit map is arranged as a l ink~d List of logicc"l blocks. The
number of blocks that the map occupies depends on the device.
It is
. ,:rea·ted by the util ~ty '~ERO' convnand. Only the first 64 worrjs of
~ach

map block have meanlng.

WORD
+~~-----~-------~---------+

:t _ LINK
TO ,....NEXT
MAP .BLOCK
... _________
__ ..._____
_______ I

.
:* ....MAP
NUt13E
R
,....-:_.. ........._ ........ _' _______________. 1'

. 60(10)

t ____ .... _ .... _____ .. _ ..._______ '___ f

LINK
TO____
F1RST MAP
___
_ __.

...,~

c . . . . _ _. . . . _ _ _ ' _ _ _ _ _ . . . _

•

! MAP fOR BLOCKS 0-15 (10)!

MAP fOR BLOCKS 16-31(10)!
.

~MAP fOR BLOCKS 944--959 (l O!

t _._ _ _ _._..._ ...._ _....'_ _ _ _ _ _ _ _ _ _ _ _ _ f

1 _ _ -___________ ..-_'-' ___________ I

.
I

+~--~-~-----~-------------+

The Logical block number of the next map
if it 15 the tast map.

block contains zero

Which map this )ne is.
- Number of words used for map.

- The logical blo~k number of first bit map.
Bit is set when block is used.
cteared when block is free.
65-25~ -NOT USED.

Word,£ ,:)-64

- Map for 960 blocks.

Bit

M 1

4.1.4

Page 10

Random Access Device Information
1

1ST UFD

MNEft10NIC

II Or UFD
BLOCKS

aLOCK 1/

1ST BIT

II OF
MAPS

MAP eLK

MFD 1

MFD2

- ...............--.....~- t --'----.-.-- i ....--------- i --------- i ------- ; ------ .1------,.
173.
1
170.
50.
DB
2
,,...~
~IoiiJI!t,
i ...........'. . . _-...-.,..- i ----....----..- i ---------- i --------- t ------ i ------ f - - - - - - f
01::.
3
16.
4795.
5.
1
4794. !
_"'"""-.....~_<M,.. .... i ~...'. . . . . .-....------...
t - ... -------- i --...------ i --~--- i ------ f - - - - - - i
l2
146.
1
2
22.
Dl
24.
t ... -------- j ---------- i --------- t --.---- f ---, - - - , - - - - - - i
,7
1
31.
96.
29.
2
i
~ ...,-...... . ., ... ". ". . . , 1-'---~-..-.-...-- ; .-.---------1-------.--- j --------- , ------ : ------ i ------ •
.
.
'RP02 .. ;
OP
3
I
170.
173.
t
50.
1
2
~~ .....~~~~ f -~,-- ... ---..... ! _ . . . - ....._-... - ... ; ...--------- i -----.... --- i ------ i ------ i ------ i
....
170.
1
50.
DR
52.
c:.

...

. . . __

1-------'--

"i , - - , - - , - - , _ ....

~~'...."--"--; .......,-~......... ...,.--....-

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

4
3
DS
"'"-..... ~--,-.... i ~.-.~~.............. 1... . . . --.-..---. ..... ~ _. ._-_... --""-_ ..... i __

...

~·.~L

. 102

trY

104

i ------ i ------ i ------ ~

100
101
j ---......... .-.-- _.... j - - - - - - - - - - t ... _--.... ---.- i ------ i -_ .... _-- i "-----.... t

. . . . . . . . . . . . --. . -. . -- .
1

7
ioIiIiI _ _ _ "-' _ _

3
3

16.

"""" ..........',. . :...o..r-.........__ ......,....-~ _ _ _ ,_ _ • - - - - - - - - - ... - - - - - - , - - - • -

19.
________ • -

_ _ _ _ _ • _ _ _ _ _ _ ...... _ _ _ _ _ "

SEQ 0012

II OF

vI f
-N-..., ..... -

BlKS

BLKS TO
PREALLOCATE

ON OEV

..... -~ ...... T-~

BOOT

INTERlEAVF

II OF

N 1

MONITOR
BLOCK II

BlK II

......'--~ ... - -... T--.................. ----. .. --... T-'"""'-... - ....... - i ... --- ---T-. . --- ... --- - T

40.

511.

. . . --,"'"""-......-,-- t -~-....-"'-'------ i ...---...~ ..__ .... _-....-- j - - - - - - - - i ------- i ---------

255.

48000.
_"""".1!100;0~ .......,_,_ ~ ...,-_ ...._._ ........ _--, -

- -....... '""""-,-"""""- t -

4800.
.... - - , - - - - - - - ... -

1 0200.

69.

200.

- - - - -..... - . - , - t - ...... - - , - , - , - - - - - 1 - - - - , - - - - - - - - - -

157.

,,7104.

223.

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

.1-------------- j--------j

20460. OR!

170.

r -------- t ------- t ----------

. . .

127.

--------,-----------1--------------,--------,-------1--------' .

48000.

255.

223.

--------;-----------;"-------------j--------j-------j---------i
1.8000.

235.

222.

--------:-----------;--------------;--------;-------;---------i
989.

41.

-----~-~-~~--------~~~-------------j--------i-------i-------~-i
..".
.
1

:> 76.

6t}.

.
I

....,,:;;,"'"""-_-.--. . . ~ ........ ...-.-..-....------.-- i -------------- i ......,---"'''''--- i ------- i --------- i
40.
1
494.
8.
----,-- - -- j -,-- .... - - - - - - - i -------------- i -------- i ------- , -----.. ---- t
~ ))'
988 .
S:) .
1
o
23.

-------- ----------- -------------- --------

SEQ 0013

r---·-·. . -.,. . . ----.--,----. . . _. _. . . .-.. .
~-

Page 11

14.2 Sequential Acce;s Devices
I

14.2.1

Magtape

Il'Althou9h magtape is not usually considered as a file structured device.
certain structure features are impleMented to enabLe creation and
retrieval of multiple tiles.

The files on maatape are terminated by an end-at-tiLe mark (EOF) or
tape mark (TM).
The last file on the tape is terminated by 2
consecutive EOFs to indicate logical-end-of-tape.

Each file on magtape is made up of a header and data records.
~ HEADER
~ lRG ! DATA RECORD! IRG ! DATA RECORD! lRG ! EOF ! IRG !
! 7 WORDS !
! 256 WORDS!
! 256 WORDS!
:
~
!

+~~---~~---~~-~-~--~--~----~-~---~~~--~~~~-~------------~~----------.

The header record is structured as fOllows:

WORD
FILE NAME
·l ___

FILE EXTENSION

!! ____ ......... 401
_..... ."........ _ ...
!
0

!!
!

~~~~~_.~~~~

~~t

~~~~~-~~-~~-----~-~!

·! FILE DATE
! FlLE SIZE

oiiIiiIi.-., ....

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

The filename and extension encoded in RAD-50.

Word 4

- D05-11 UIC [1~lJ

!,v'ord 5

- Set to zero.

Word '1

5
6

I_~~._~~~~~.-~~~~.~,

Word 1. 2 and 3

.
!

I_~~~~~~~~-~~~~~~-._I

word 6

.
.~

Date given the file when written on the tape. It is in
D05-11
format.
c,'t 15 of the date. when set.
indicates a cortiguous file •
... The nunber of logical blocks (records) in the file.

The first file on a magtape is normally the XXDP+ monitor core image. It is
written as a contiguous fHe. Every new file is written at the logical end
of tope. The t.ast fHe on tape may be written so part lies aftf;,'r the physical
. Eor marker but no tHe wilL be written entirely after the physicaL EOT mark.

Sf Q 00 .:.

C 2

,The number of fiLes that a magtape can accommodate is a functfort of the file
sile~ the drive density and the tape length.

L,"__ "_"_'"__,,_~~___,___.~.____,~_"___,____,_'. -.~~-....-,--"",,-" -~.""-,.. --".".,". -.-"-."-"". --"-,-,--. -".-,-"-",.-,_..._.... '....... ',..."-

SEQ 0015

4.2.2

Cas~ette

Page 12

(TU60)

(asset ~e is st rue tured s imilari ly to magtape if I that each f i l e ; s
preceded by a header and a marker that identifies the logical end of
tape. However. the actua~ data in the header and end-ot-file marker
are d i f ferent •
The files on cassette are terminated by a file gap. The last file on
! the
~ape ,is terminated by a sentinel fi~e •. A file gap mus..; precede
the flrst file on the cassette. The tape 1$ formatted as follows:
! GAP! FILE A ! GAP! fILE B ! GAP! F.1LE r ! GAP ! St;NTlNtL !

the sentinel file is a 32 byte record ct,ntaining all ~ero·s.

lEaCh file on cassette is made UP of a file header record and file data
records in multipLes of 4.
'
~

fH,E HEADf:P ! DATA RECORD J DATA flECORD ! DATA RfCORD ! DATA RECORD! GAP!
32 BYTES

128 BYTES

128 SYTES

128 BYTES

128 BYTES!

SEQ 0016

E 2
SEQ 0017

The fHE' h$ader record is structured as follows:

BYTE

fILE NAAE

t ____ .'.--...,.' ___ • ____ .....

'1-6

1
r H.E EXTENSION !
, ...........'. . ._,. . . .-. ___ ......... f

7,8.9

i FILE TYPE _.II.'.. ___ ~t
!! ____
100000
!~

l ___.. _ . ___ ._..

...

11, 12

IIIMi: . . . . . . . . . . . '. . . . . __ . . . . . . __ . . .

!! .......... _.........
0

.._...._' ___ ... !
!t _,.. __
DATE
,__ ...... ____ .................. !t

13-16

'19.20

. fILE LENGTH

"'!Iiit. :

17,18

!
:~~~-~-----~--.*---!
!
0

21,32

Bytes 1...9

.... F i len~ arid extens h)n encoded in RAP-50 .

eyt~

.... File type indicator.

Bytes 11. 12

0=6000

14=Deleted.

... Word indicating tf?cord length set to 100.000 (128
r~(Qrd$) •

byte

.... S.q~rH:e rn.lT4bt'lr not used in XXDP+.
eyt~

... Header continuat ion not I.Jsed in XXDP+.

fjyt.s 15 j 16

.... Not ustd.

a.ytes 1....f,. ""

... DOS-11 form.at ted da"e 91 v@n the file when

... Nun!).,. of log;eet blocks in tnt' file.
CCt'ltiguo'u$ f1le$ only.

byt

put

the

tape •

21-l2'" Not us~d.

for

lRG -

Interrecord gap.

Page i3

The gap that is written between records on magtape.

IMfO ... Mastffr File Directory
I

IkAD"SO - RADIX-50.word.A method of encoding 3 AS(11 characters into one 16 bit
I D ~ user File Directory.
U)C -

@r Identification code.

Sf () 001 B