ENIAC                             U. S. Army

A Logical Coding System Applied to the ENIAC


Two additions to the ENIAC have been ordered which will greatly increase its memory and flexibility. The first is called the converter. It is a device for converting any two-digit number to a program pulse in one add-time. This will make available 100 pulses for orders instead of 60 and will, in addition, free the master programmer for other uses. The converter has already been delivered and has already been used to modify the 60-order code in such a way as to save space in the function tables for shifts (i.e., there are 19 2-digit shift orders instead of 1 4-digit shift order) and to make it possible to take orders from cards as well as from the function tables.

We shall not describe this modified code in detail since there will be a better code available by the time this report is available. The better code will use not only the converter but the other addition called the register.

The register is really a set of one hundred ten-digit registers with three operations: It can clear its old argument and receive a new argument in one add-time; it can receive a number, clear that register designated by its current argument and send the number to that register, increasing its argument by one; it can send out (and also keep) the number designated by its current argument. The latter two operations consume three add-times.

With the converter and register it will be possible to achieve among others the following results which will be incorporated in a new code to be described when completed:

  1. Increase the speed of the ENIAC considerably.
  2. Increase the efficiency of the orders; that is, the amount of computation per unit space in the function tables.
  3. Store orders in the register and thereby make it possible to control computations with cards and to modify orders for inductive processes.
  4. Use the additional memory to solve problems involving more numbers, e.g., solve a system of thirty ordinary non-linear differential equations.
  5. Use the card control to facilitate testing and demonstrating the ENIAC.

A first form of this new code should soon be available and the ENIAC should be ready to use this code by December.