Slide 39 of 89
The Thornton book is really great because it contains both the design philosophy and the design. It describes their quest for both speed through circuitry and parallelism. It is also a must read for every computer architect.
One principle was that all parts of the computer should operate asynchronously and independently. To begin with all IO devices could independently. Next any IO channel could be assigned to any IO device so that the channel doesnít become a bottleneck. Finally, any IO Channel could be assigned to any of the ten IO Peripheral Processing Units or PPUs. PPUs were totally independent 12 bit computers similar to the CDC 160. All PPUs could transfer data to the central memory. There was unbound flexibility for the transfer of data into the large computerís memory. Of course the central memory was accessed by the main processing unit where all the floating point computation was carried out on 60-bit words.