Chapter 9 The design philosophy of Pegasus, a quantity-production computer 175

problem then was to arrange the various circuits in such a way as to enable a computer to be designed using a minimum total number of packages without too many types. Five types were arrived at and these are shown in Fig. 6.

As an example of the factors involved, consider package types 1 and 2. The circuit units based on package type 1 can perform all the functions of those on type 2. However, there are many uses for a digit-delay circuit with a single 'and' gate input (package type 2), and since three units of this kind (instead of two for a 2- 'and'-gate input delay) can be based on one package, a saving can be effected. In Pegasus this saving amounts to 32 packages, which is considered to be well worth an extra package type.

In addition to the five logical packages, a further 16 types (three of which are peculiar to each computer) are required. The numbers used for the various functions are given below: