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Further reading □ Overview □ Brochures □ ICT 665 printer (1960) □ Ampex TM-2 tape deck (1961) □ Anelex printer (1961) □ Creed 300 tape punch (1961) □ Papers: 1960 □ Users' specification □ Punched card codes □ Description of the Ferranti Atlas □ IBM magnetic tape □ 1961 □ Peripheral equipment □ Punched tape codes □ Magnetic drum □ Operating System □ IBM tape control logic □ Paper tape input □ Operator's I/O □ 1962 □ Memo on extracodes (April) □ Memo on extracodes (May) □ Primary Supervisor □ Intermediate Supervisor □ Notes on Extracodes □ Monitor program □ 1963 □ Processing commercial data □ Magnetic tape □ Intermediate supervisor □ Alternative monitor action □ Non-standard peripherals
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⟶ ACL ⟶ Literature ⟶ ACL Publications :: Early Atlas Documents
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Further reading ⇓

□ Overview
Brochures
□ ICT 665 printer (1960) □ Ampex TM-2 tape deck (1961) □ Anelex printer (1961) □ Creed 300 tape punch (1961)
Papers: 1960
□ Users' specification □ Punched card codes □ Description of the Ferranti Atlas □ IBM magnetic tape
1961
□ Peripheral equipment □ Punched tape codes □ Magnetic drum □ Operating System □ IBM tape control logic □ Paper tape input □ Operator's I/O
1962
□ Memo on extracodes (April) □ Memo on extracodes (May) □ Primary Supervisor □ Intermediate Supervisor □ Notes on Extracodes □ Monitor program
1963
□ Processing commercial data □ Magnetic tape □ Intermediate supervisor □ Alternative monitor action □ Non-standard peripherals

Provisional Specification of IBM Tape to Atlas Control Logic

21 August 1961

1. The following basic functions can be performed directly by the control logics

  1. Read - transfer the next record from tape to Atlas
  2. Write - transfer the next record from Atlas to tape
  3. Backspace - move the tape backwards one record.
  4. Set Low Density - set packing density status to Low
  5. Set High Density - set packing density status to High
  6. Rewind - rewind the tape to load point
  7. Disengage - disengage the tape unit from Atlas.

2. Transfers may be in any combination of High/Low density and Binary/BCD mode.

3. The Tape Control logic will consist of one read/write channel such that only one of the functions Read Write, Backspace, Set High Density, Set Low Density or Disengage may be in progress at any one time. However rewinds, if previously initiated, may be in progress simultaneously on other tape machines.

4. Up to three IBM 729 Mk IV tape mechanisms may be connected to the tape control logic.

5. Character conversion will be done in the BCD mode for both read and write transfers.

6. Performance of the 729 Mk IV tape mechanisms limits the maximum rate of reading or writing records. Time for a high density write transfer is (7.8+0.016n) mS where n is the number of characters in the record. For 16 word (128 character records this is 11.2 mS resulting in a maximum record rate of less than 90 records/sec.

7. Reading and writing transfers will be fully redundancy checked with separate error indicators for lateral and longtitudinal redundancy.

8. Should a read or write transfer conclude with a part-word, a count indicating the number of significant characters will be sent to or from Atlas, respectively.

9. Atlas routines will control all magnetic tape operations, sense the various indicators, and exert supervisory control.

Interrupts

1. Buffer Attention Look-at-Me

Set up as required by tape control during a read or write operation to indicate that information must be transferred between Atlas store and the information buffer. The BALAM interrupt routine performs the required transfer and resets BALAM (with POBALAM)

2. End of Operation Look-at-Me

Set by tape control at the end of each operation, as follows:-

  1. Read,Write and Backspace: After last position
  2. Set High, Set Low Density, Rewind and Disengage: When a relay closure return signal operates in the tape machine (about 10mS).

EOLAM indicates that the previous operation is complete so far as the tape control is concerned, and that the next order may proceed.

Resetting is done by the EOLAM interrupt routine (POBOLAM).

3. Mechanical Failure Look-at-Me

Set up by tape control as follows:-

  1. When the selected tape unit does not respond to control signals of an order. In this case execution of the order is inhibited.
  2. During a write operation when a write echo failure occurs. It is reset by the MFLAM interrupt routine (POMFLAM).

4. Rewind Complete Look-at-Me

Set by tape control when any of the tape units come to a halt at the conclusion of rewinding. Simultaneously one of three lines (Rewind Complete TU1, TU2 or TU3) will be set in the V-store to indicate the tape machine referred to.

Provision will be made to deal with simultaneous completion of rewind on any number of tape units.

LINES BETWEEN TAPE CONTROL AND ATLAS

          2 x 48 Information
Wl	1 (Select TU1
Wl	1 (Select TU2
Wl	1 (Select TU3

Wl	1 (Read
Wl	1 (Write
Wl	1 (Backspace
Wl	1 (Set High Density
Wl	1 (Set Low Density
Wl	1 (Rewind
Wl	1 (Disengage

   Source in Atlas
   
Wl	1 (Binary Mode
Wl	1 (BCD Mode
Wl	1 (Stop Write
Wl	1 (PO BALAM
Wl	1 (PO EOLAM
Wl	1 (PO MFLAM
Wl	1 (PO RCLAM
   
   Source in Atlas and Tape Control
   
RW1 4  Character Count                          )

   Source in Tape Control
   
R1  1  Buffer Attention Overdue                 ) Reset by Tape Control
R1  1  (Lateral Parity Failure                  ) as each order is
R1  1  (Longtitudinal Parity Failure            ) sent to it
R1  1  Tape Indicator                           )

R1  1  (Rewind Complete TU1                     )
R1  1  (Rewind Complete TU2                     ) Reset by PORCLAM
R1  1  (Rewind Complete TU3                     )

R1  1  Load Point Indicator

R1  1  (TU1 engaged
R1  1  (TU2 engaged
R1  1  (TU3 engaged

Total 32 lines

DESCRIPTION OF INPUT/OUTPUT LINES

Select TU1, TU2 and TU3
The tape unit to be used with each order is selected by pulsing the appropriate line.
Read
An order line which causes a read operation to be performed on the selected tape unit, when it is pulsed.
Write
As above except for write.
Backspace
An order line which, when pulsed, causes the selected tape unit to move backwards one record.
Set High Density
An order line which, when pulsed, causes the High/Low Density relay in the selected tape machine to move to the High Density status (if not already there).
Set Low Density
As above, except for Low Density status
Rewind
An order line, causing the selected tape unit to rewind to the load point. The tape control may proceed with further orders referring to other tape machines once the rewind return signal operates (about 10mS)
Disengage
An order line, causing the selected tape unit to be disengaged from Atlas (returned to manual status). Note One, and only one, order line may be pulsed to specify each order.
Binary Mode
When pulsed this line causes future transfers to all tape units to be carried out in the binary mode.
BCD Mode
As above, except for BCD mode.
Stop Write
Pulsed by Atlas when, and simultaneously with, the transfer of the last word (or part word) to the information buffer, for a write operation. The character count is also transferred at this time.
POBALAM
Pulsed by BALAM interrupt routine to reset BALAM (which caused entry to the routine)
POEOLAM
As above, except EOLAM.
POMFLAM
As above, except MFLAM.
PORCLAM
As above, except RCLAM.
Character Count
(i) Read: Set by tape control to indicate the number of significant characters in the last transfer of a read operation. The count is transferred to V-store in parallel with the information bits.
(ii)Write: Set by write extracode simultaneously with the last transfer of information to be written on tape (and also Stop Write), to indicate the number of significant characters.
The character count is reset by the tape control as each new order is sent to it.
Buffer Attention Overdue
Set by tape control if information is being destroyed due to the inability of the BALAM interrupt routine to transfer information to or from the buffer in the required time, Reset by tape control as each new order is sent to it.
Lateral Parity Failure
Set up during a read or write operation by tape control if a lateral parity check failure is detected* Reset by tape control as each new order is sent to it.
Longtitudinal Parity Failure
As above, except for longitudinal parity failure.
Tape Indicator
Read Transfer: Set by tape control when an End of File mark is detected.
Write Transfer: Set by tape unit when End of Tape mark is photosensed.
Reset by tape control as each new order is sent to it.
Rewind Complete TU1
Set by tape control when TU1 completes a rewind operation. RCLAM is also set at the same time. Reset by PORCLAM.
Rewind Complete TU2
As above, except TU2.
Rewind Complete TU3
As above, except TU3.
Load Point Indicator
A signal which is in the one condition if the selected tape unit is at the load point.
TU1 Engaged
Set if TUl is loaded with all interlocks closed and the Start key has been pressed. It may be reset by a Disengage order from Atlas, or by pressing the Reset key.
TU2 Engaged
As above, except for TU2.
TU3 Engaged
As above, except for TU3.
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