IBM 2365 Processor Storage
The IBM 2365 Processor Storage was a component of the IBM System/360 models 65,[1] 67,[2] 75[3] and 85[4] computers. Storage was implemented using magnetic cores, and the storage width was 72 bits, which comprised 64 data bits (8 bytes, or one doubleword) plus 8 parity bits. The IBM 2365 model 1 contained 131,072 bytes of memory; all other models contained 262,144 bytes. The model 2 could be converted in the field to a model 13.
All models other than the model 1 consisted of two memory stacks. Addressing for the stacks was interleaved, so the first 64-bit word was in one stack, the second in the other stack, and so forth. This improved performance when doing sequential access.
All models other than the model 5 had a cycle time of 750 nanoseconds.
Models
The various models were used as follows:
- Model 1 was used on the System/360 model 65 when not used as a multiprocessor.
- Model 2 was used on the System/360 models 65 (when not used as a multiprocessor) and 67-1.
- Model 3 was used on the System/360 model 75.
- Model 5 was used on the System/360 model 85.
- Model 12 was used on the System/360 model 67-2.
- Model 13 was used on the System/360 model 65 when used as a multiprocessor.
Use with the System/360 model 85
The IBM 2365 model 5 was special because the System/360 model 85 was a 128-bit machine, unlike the other System/360 models which supported the IBM 2365, all of which were 64-bit machines. On the System/360 model 85, the IBM 2365 model 5 operated with a cycle time of 1040 nanoseconds, and two or four of them were required. Because the System/360 model 85 CPU was so much faster than memory, if there were two IBM 2365 model 5 components they were two-way interleaved, and if there were four IBM 2365 model 5 components they were four-way interleaved. Because the IBM 2365 model 5 was internally two-way interleaved, sequential 128-bit memory operations issued by the System/360 model 85 CPU would traverse all the memory components before cycling back to the first.
The IBM 2365 model 5 was used only with the System/360 model 85 with 524,288 or 1,048,576 bytes of storage. Models with 2,097,152 or 4,194,304 bytes used the IBM 2385 instead, which had a cycle time of 960 nanoseconds.
References
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