Tapes may be classified in a number of ways.
These tapes are the standard form of storage for routines and other large blocks of information. One tape is made for each half track, and takes the form
The punching proper results in transferring certain information to page 4, the `systematic working space'. It will normally be punched with the `J' meaningful sequences.
The check sum is the sum of the long lines of page 4 after the punching proper has passed through.
The writing tapes are intended for use with the routine WRITE. If this routine is entered when the beginning of a writing tape is in the input, the title will appear in the output and the information in the punching proper will be written in the appropriate half-track, after a number of precautions have been taken, including a check on the track-selection mechanism, verification that the correct check sum is formed, and a check that no digits were altered in the writing process. For further information on this routine its official account must be consulted.
Writing tapes should normally be produced automatically from information within the machine. The routine for this purpose will shortly be available, but details are not yet known.
It is intended that a typewritten list be kept of all tapes with their titles, destination sequences and check sums, i.e. essentially all of the tape except the punching proper.
It is convenient to use INPUT, in combination with an appropriate tape, as a master routine for a job. In so far as the master routine is non-repetitive this is no slower than putting a master routine away in the magnetic store and then entering it. The advantages of this method, when applicable, are
Even when a certain amount of repetition is involved it may be less trouble to have repetition e.g. by copying on the tape rather than to attempt to produce a routine in which the repetition is achieved by passing through the same instructions again and again. An example of this is described in the appendix (p. ).
Exercise. Suppose that ££ABF/EZ is the cue of a routine whose effect is given by , and does not alter any long lines, except the conventional ones and :C, produce a job steering tape for printing out the values of for six given arguments. Use OUTPUTA.
The twenty digit rows that are put into a cue-bearing track to assist the routine changing sequence in turning false cues into true cues may be called `tape addresses'. For every job it is necessary to assign an address to each tape involved. The list of these addresses or directory has to be put into the cue bearing tracks (which should be very few) before the job can begin. This process is certainly something of an imposition. It is hoped that it will be possible to have a small number of standard directories of which one will be suitable for almost any job. Those routines which are special to the job may be given true cues and will not need directory entries.