IBM 2361 Large Capacity Storage
| Company type | Computer hardware |
|---|---|
| Industry | Computer storage |
| Founder | International Business Machines Corporation (IBM) |
Area served | IBM System/360 models 50, 65, and 75 |
| Products | Large Capacity Storage (LCS) units, model 1 and model 2 |
| Owner | IBM |
| Parent | IBM |
The IBM 2361 Large Capacity Storage (LCS) serves as an optional memory expansion unit compatible with IBM System/360 models 50, 65 (provided it is not configured as a multiprocessor), and 75. This device employs magnetic core technology, featuring an 8-microsecond cycle duration and a 3.6-microsecond access latency, which is slower compared to the primary storage—for instance, 8 microseconds versus 750 nanoseconds on the Model 65. Also referred to as IBM 2361 Core Storage or Large Core Storage, it offers supplementary main memory capacity.
NASA incorporated the IBM 2361 into their IBM 7094 real-time computing system, adding 524,000 words of 36 bits each to its memory resources.
Description
The IBM 2361 is available in two variants: model 1 provides 1,048,576 bytes (1 MB), while model 2 offers 2,097,152 bytes (2 MB). The model 2 configuration includes 64 core planes of 32 KB each, representing the largest core planes ever produced.
This storage unit can be shared between two System/360 machines. When shared between pairs such as two model 50s, two model 65s, two model 75s, or a combination of model 65 and model 75, both systems are required to have equal amounts of main memory. In cases where sharing occurs between a model 50 and either a model 65 or model 75, the model 50 may possess less primary storage.
If the system contains an even number of IBM 2361 modules and includes at least one processor of model 65 or 75, these units can be configured in an interleaved arrangement to improve sequential data access. Interleaving distributes data alternately across units so that while one completes its cycle, another begins processing the next data segment.
Configurations allow either a single model 1 or four model 2 units in a non-interleaved setup, or two model 1 units or four model 2 units in an interleaved mode. This arrangement can deliver up to 8 MB of additional memory capacity—particularly notable since the Model 75J supports only up to 1 MB of processor memory.
Software support
Within OS/360, users have the option to allocate memory either from processor storage ("hierarchy 0") or from the slower LCS ("hierarchy 1"). Memory region sizes can be defined via JOB or EXEC statements using the syntax: REGION=(VALUE1,VALUE2), where VALUE1 specifies processor storage in kilobytes and VALUE2 specifies LCS storage. Several system macros permit designation of storage hierarchy preferences. The macros ATTACH, DCB, GETMAIN, GETPOOL, LINK, LOAD, and XCTL include a parameter (HIARCHY=n), where n can be either 0 or 1. Additionally, the OS/360 linkage editor supports a HIARCHY control statement that allows assignment of specific control sections to one of the hierarchies. This capability enables programs to distribute sections between processor storage and LCS, facilitating the loading of large but infrequently accessed program components into LCS and thus enhancing overall memory efficiency.