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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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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

ATLAS Input of case and shift characters from paper tape

C.R. Merton

9 October 1961

  1. It has been proposed that when reading- 7-track paper tape, the Atlas system should not store characters representing upper-case and lower-case, but only allow for their effect on the characters which follow; and similarly with letter-shift and figure shift on 5-track paper tape. This would not apply when reading in the binary mode, and it would still be possible to output the characters concerned.
  2. Alternatives which have been suggested are as follows:
    1. All characters read are stored. This would be particularly wasteful with some types of data if the internal representation of case of shift characters appeared either only in the inner set or only in the outer set.
    2. A case or a shift character is only stored if it is not implied by the current case or shift and the next character. Examples may make this clear (here it is assumed that space occurs in both sets but shift characters only on inner set). 
      Paper tape (7-hole)           Store 
A lower-case a                A shift-out a 
A space lower-case a          A space shift-out a 
A lower-case space a          A shift-out lower-case space 
A upper-case A                A shift-out upper-case shift-in A
      In the third example the lower-case character must be stored because the space character occurs in both sets, so that the lower-case is not implied by it. This convention would require that no case or shift character were finally stored until the next input character had been recognised, but enables an exact copy to be output of a tape which has been input.
    3. Only that case or shift character is stored which is used for run-out, and the amount of run-out is perhaps indicated in the next character stored. This does not allow an exact copy of a tape to be output, and would be unacceptable when a non-standard code was being used unless the case or shift characters had their standard significance.
  3. Advantages claimed for the proposal outlined first are as follows:-
    1. The paper tape is a representation of the printed page, and should not contain any information which cannot be obtained from it. Against this may be made the following points:
      1. The same printed line may be punched in various ways using space, tabulate and backspace function characters; for instance extra spaces may be punched at the end of a line and would be stored in any system proposed. The proposal therefore fails in this objective.
      2. It is often very valuable to be able to store information in a punched paper tape which does not appear in the printed representation, and punching conventions using this facility have been found convenient and reliable. Examples are label termination, inter-record marks and end-of-tape marks.
      3. Machines which produce punched paper tape often produce a print-out which is not an entirely reliable representation of the paper tape; it is not therefore adequate merely to check this printout in any case.
    2. Storing shift or case characters is a waste of computer storage.
      1. It is unlikely that there would be any significant advantage over alternatives 2b or 2c except in the case of run-out. It may be suggested that any data preparation department which produces large quantities of paper tape on which more than 10% of the characters are run-out might find it difficult to justify this practice.
  4. A further disadvantage of the proposal first outlined is as follows:-
    1. In the case of five-hole paper tape in standard Ferranti or B.S.I. code a parity check on numeric characters may be done by program; and if the blank run-out character is not stored it is likely that errors will not be detected.
  5. It may be pointed out that all these difficulties may be got round by using the binary mode for input of paper tape. This, however, has considerable disadvantages:
    1. Unless the tape has been prepared on a computer, it unlikely that its exact length would be known as required for efficient use of this mode.
    2. It is wasteful to read a tape prepared in a 7-track odd-parity code on Atlas without utilising the built-in parity checking facilities.
  6. I therefore submit that while the proposal may be acceptable for the University's internal work, it is not applicable more generally.
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