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Document:	PDP-X Technical Memorandum #11 DECtape tape format
Order Number:	XX-B6A97-34
Revision:	0
Pages:	5
Original Filename:	11.pdf

OCR Text

'
PDP-X Technical Memorandum # 11
S
‘

Thirs drawing and specifications, herein, are the prop

not be
erty of Digital Equipment Corporation and shall
reproduced or copied or used in whole or in part as
wnthpu{
the basis for the manufacture or sale of |tems}

| written permission-

Title:
.

—DECtape Tape Format Considerations

(s) : S.
Author
Index -

Keys:

Booth

DECtape Format

DECtape
1/0

Peripherals

Distribution
Keys:

Obsolete:

None

Revision:

None

Date:

July 18,

1967

Introduction
A.

This memo contains come comments and suggestions con. cerning the PDP-X Dectape Tape format.
It does not
consider I/0 commands

status words.

Three points are considered

1. Basic quantum of parallel transfer

II.

Data

Block Structure

Other

considerations

Basic Quantum of Parallel Transfer

fThe_8'bit—byte is a unit compatible with -the Multi.plexor Channel,

-fore,

I/0 Bus,

it could be

Assuming

the

which

format

8 bit-byte

8 bits

(plus

reasons

stated

format,

PDP-9

C. - "Given

the

uses

three

parity

later.-

format,

format

and other

desirable

I/0 devices.. There-

for Dectape.

tape

desirable)

seems
1.

Figure

the

record

desirable

compares

proposed

suggested in Sec.

PDP-X

II.B.,

two

PDP-8.

Read/

of assembly/disassembly are desirable.

Mode

transfer

mode

lines

one

byte.

and would be

ance,

Three

used

interchange,

tape
This

for

are

assembled

would

all

the

PDP-X

formatting

for'

format.

Write Modes

the basic unit of transfer,
lines

The

and

for

normal-

non-mainten-

operations.

Mode 2 - Two lines of tape are assembled
for
transfer

one

byte

g - MR

TRK

BIT

TRK

BIT

INFO
"t

the

following

format:

4 - MR

TRK

BIT

5 -

TRK

BIT.
&

—

INFO
n

:Thé two modes allow all necessary read/write opera-tions

to be performed

‘transfers,
and

PDP-X

for

inter-

and

PDP-X tape formatting,
to

other

PDP

intra-PDP-X

PDP-X diagnostics,
..

transfers

with

all

information

‘obtainable.
1.

PDP-X

System Usage

PDP-X

Tape

PDP-X Diagnostics

PDP-X Write,

(probably Mode l)
5.

',II:°

Mode

Formatting

Mode

- Modes

Other

PDP-X Read,

PDP

Read

Mode

l or 2

Other PDP Write - Mode 2

VDafa”Block Structure
A.

Based

blocks

PDP-8

128

PDP-9

256

usage

words

and

the

appears

PDP-X

include

new programming

for

storage

devices

other mass

(e.g.,

field

desirable.

.considerations
drum) .

IV.

size,

Other

file structures
.
disc,

mag

tape,
-

Related Considerations
A.

-Data Density Reduction - The 11% of unusable storage(1

bit

unused

hardware

for

a.Yeasonable

,Dectape
to

traded

not

for

assembly/disassembly.
trade off

since

storage is "low".

access

would

out

given

block

realized

reduction

This

the dollars

seems
per

11%decrease

still

very mamy

"long"

in.

like-

bit of
-

the time

time

and.

turnarounds were

TYequired.

tAssembly for Mode
required

for

1 and Mode 2-additional

two modes

assembly,

logic is TM

however,

this

buys:
1.

A method to format tapé,

A method

smooth

appearance

for

tape

PDP-X machines.
sity

(e.g.

“hardware

(e.g.

to the

program.

commmnication with

Other methods

% using two

cost

tracks

8 bit—-—18 bit

non-"

in den-

only) and

transform)

also.

With a ROS program running the tape control the
additional hardware cost may not be

When available,
)

significant.

a clearer definition of the I/0

Processor could clear up this point.

C. Transfer Timing - With single byte buffering in the
control the maximum time between byte transfers in

Mode 1 is

( 3 lines X 33.3 ps/line)-30% = 100 ps - 30% =

approx.

ps.

In Mode

this

time 1is

System usage should be Mode 1 and 70

present no unreasonable restrictions.
require

the 46

limit.

approx 46 ‘us.

ps worst case

should

The TCFl & TC@2

’

D. Write/Read in Opposite Directions - Would a ROS controller
provide
users

this

feature cheaply?

make use

it?

Would the
,

system and

Timing Track
Mark

Track

nformation Track

PDP-8

10 | 1

811 2 5

PDP-9

l§ 4 .

I
|
9 12 15
0. 3:

8.1l

811

?
15

10 13 16

11 14 17

P 10 13 .

1
i

PDP-X

§ 11 14

}

2 1 4 7
9115

Byte 1l

i
'

Byte

12,15 1! 4,

Figure