as fast as possible. CDC's approach in the STAR used what is today known as a memory-memory architecture. This referred to the way the machine gathered data. It set up its pipeline to read from and write to memory directly. This allowed the STAR to use vectors of length not limited by the length of registers, making it highly flexible. Unfortunately, the pipeline had to be very long in order to allow it to have enough instructions in flight to make up for the slow memory. That meant the machine incurred a high cost when switching from processing vectors to performing operations on non-vector operands. Additionally, the low scalar performance of the machine meant that after the switch had taken place and the machine was running scalar instructions, the performance was quite poor. The result was rather disappointing real-world performance, something that could, perhaps, have been forecast by Amdahl's law. Cray's approach Cray studied the failure of the STAR and learned from it. He decided that in addition to fast vector processing, his design would also require excellent all-around scalar performance. That way when the machine switched modes, it would still provide superior performance. Additionally he noticed that the workloads could be dramatically improved in most cases through the use of registers. Just as earlier machines had ignored the fact that most operations were being applied to many data points, the STAR ignored the fact that those same data points would be repeatedly operated on. Whereas the STAR would read and process the same memory five times to apply five vector operations on a set of data, it would be much faster to read the data into the CPU's registers once, and then apply the five operations. However, there were limitations with this approach. Registers were significantly more expensive in terms of circuitry, so only a limited number could be provided. This implied that Cray's design would have less flexibility in terms of vector sizes. Instead of reading any sized vector several times as in the STAR, the Cray-1 would have to read only a portion of the vector at a time, but it could then run several operations on that data prior to writing the results back to memory. Given typical workloads, Cray felt that the small cost incurred by being required to break large sequential memory accesses into segments was a cost well worth paying. Since the typical