The IBM System/360 Model 91 was announced in 1964 as a competitor to the CDC 6600.
The first Model 91 was used at the NASA Goddard Space Flight Center in 1968 and at the time was the most powerful computer in user operation. It was capable of performing up to 16.6 million instructions a second.
The CPU consisted of five autonomous units: instruction, floating-point, fixed-point, and two storage controllers for the overlapping memory units and the I/O data channels. The floating-point unit made heavy use of instruction pipelining and was the first implementation of Tomasulo's algorithm. It was also one of the first computers to utilize Multi-channel memory architecture.
There were four models They differed by their main memory configuration, all using IBM's 2395 Processor Storage.
The 91K had 2 MB, using one 2395 Model 1.
Both the 91KK and the 91L came with 4 MB of main memory: the former used a pair of 2395 Model 1s, the latter a single 2395 Model 2.
The 6 MB KL was equipped with one Model 1 and one Model 2 IBM 2395s.