Proposed Electronic Calculator/Chapter 7
7. External Organs.
(i) General.— It might appear that it would be difficult to put information into the calculator and to take it out, on account of the high speeds associated with the calculator, and the slow speeds associated with mechanical devices; but this difficulty is not a real one. Let us consider for instance the output organ. We will allow the mechanical part of the output organ to work at whatever pace suits it, to take its own time in fact. However we will require it to give out signals stating when it is ready to accept information. This signal provides a gate for the feeding of the information out to the output organ, and also signifies to the calculator that it may note that information as recorded and proceed to feed out some more. The preparation for feeding (p.384) the information out consists merely in transferring it from dynamic storages onto trigger circuits.
In the case of the output arrangements we have the full power of the calculator behind us, i.e. we can do the conversion of the information into the required form as an ITO. In the case of the input organ we must go more warily. If we are putting the instruction tables into delay lines, then when the power has been turned off all memory will have been effaced, including the instruction tables. We cannot use instruction tables to get the information back, because the instruction tables are not there. We are able to get over this difficulty as will be seen below.
(ii) Output Organ.— The output will go on to 32 columns of some Hollerith cards. All the 12 rows may be used. On the receipt of a signal from the calculator a card will begin to pass through a punch or ‘reproducer’. Shortly before each row comes into position for punching a signal is sent back to the calculator and trigger circuits controlling the punches are set up. After the punching another signal is sent to the calculator and the trigger circuits are cleared. The reproducer punch also gives a signal on the final exit of the card. The circuit is shown in connection with CA (Fig. 26).
(iii) Input Organ.— Let us first describe the action of this without worrying about the difficulty concerning absence of instruction tables. It is very similar to the output organ in many ways. The input is from 32 columns and 12 rows of a Hollerith card. When the calculator is ready a card release signal goes out to the card reader and a card begins to pass through. As each row comes into position for reading a signal is sent back to the calculator, which then prepares to accept the output from the reader at the moment appropriate for sending it to its destination in the delay line. It is assumed that this destination is already decided by the calculator. A signal is sent back to the calculator on the final exit of the card.
Now let us consider what is done right at the beginning. Arrangements are made for setting into CI and CD a certain invariable initial order and IN. These state that the card is to be transferred into a particular delay line, and that the next order is to be taken from a particular spot, which will actually be in this same delay line. The information in this delay line can contain sufficient orders to ‘get us started’. The first few orders obeyed will probably be to take in a few more cards. The information on these will later be sorted to its final destination. When the final instructions are in place it will be as well to ‘read them back’.
Actually it has been arranged that the special initial order consists of 0 throughout so that there is no need to set it up.
(iv) Binary-decimal conversion. It is proposed to do binary-decimal and decimal-binary conversion as ITO.[1] This will be appreciably assisted by the fact that short multiplication is a CAO.[2]
(v) Instruction-table cards. It was explained in connection with the input organ that the instructions would be on cards, of whose columns all but 32 were available for external use. A proposed use of the 80 columns is suggested below, without proper explanation; the explanation comes later.
| Columns | |
| Genuine input | 41-72 |
| Repeat of destination | 26-40 |
| Popular name of group | 1-8 |
| Detail figure (popular) | 9-11 |
| Instruction (popular) | 12-25 |
| Job number | 73-77 |
| Spare | 78-80 |
Of these the genuine input has already been spoken of to some extent, and will be spoken of again further. The job number and the spare columns do not require explanation. The popular data describe the instruction in letters and figures in a manner appropriate for the operator to appreciate quickly if for instance the cards are listed. In this respect we might say that the popular data is like a telephone number Mol 1380 whereas the genuine input is like the pulses used in dialling: indeed we shall probably carry the analogy further and really only distinguish 10 different letters, as is done on automatic exchanges. The popular data have also another important function, which only appears when we consider that the same instructions will be used on quite different jobs. If we were just to number the instructions serially throughout all the instructions ever used on any job, then, in the set of instructions actually used in any particular job there would be large gaps in the numbering. Suppose now that these instructions were stored in the DS with positions according to their numbers there would be a lot of wasted space, and we should need elaborate arrangements for making use of this space. Instead, when a new job appears we take the complete set of cards involved and make a new copy of each of them; these we sort into the order of popular group name and detail figure. We then renumber them consecutively in the binary scale. This number goes into the columns described as ‘repeat of destination’. The renumbering may be done either with a relay counter attached to a collator, or by interleaving a set of master cards with the binary numbers in serial order. To complete the process we have to fill in other instruction numbers in binary form into the genuine input, e.g. if an instruction in popular form were “. . . and carry out instruction Potpan 15” the genuine input will have to be of form “. . . and carry out instruction 001101. . .1” where 001101. . .1 is the new number given to Potpan 15 in this particular job. This is a straightforward sorting and collating process.
It would be theoretically possible to do this rearrangement of orders within the machine. It is thought however that this would be unwise in the earlier stages of the use of the machine, as it would not be easy to identify the orders in machine form and popular form. In effect it would be necessary to take an output from the calculator of every order in both forms.