IBM 2365 Processor Storage
The IBM 2365 Processor Storage was a component of the IBM System/360 models 65, 67, 75 and 85 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.
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.
- IBM (September 1968), IBM System/360 Model 65 Functional Characteristics, Fourth Edition, A22-6884-3.
- IBM (February 1972), IBM System/360 Model 67 Functional Characteristics, Third Edition, GA27-2719-2.
- IBM, IBM System/360 Model 75 Functional Characteristics, A22-6889-0.
- IBM (June 1968), IBM System/360 Model 85 Functional Characteristics, Second Edition, A22-6916-1.
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