IBM System/360 Model 75
| Company type | Computer system |
|---|---|
| Industry | Computing |
| Founded | April 22, 1965 |
| Fate | Retired |
Area served | Global |
| Products | Mainframe computer |
The IBM System/360 Model 75 was a high-performance computer system launched on April 22, 1965, and has since been retired. Within IBM's System/360 series, it fulfilled several functions, notably acting as a top-tier main processor under the Attached Support Processor (ASP) program starting in 1967. It also accommodated various time-sharing environments, including TSO and CALL/OS. Despite its advanced features, the Model 75 accounted for a relatively minor portion of the overall System/360 sales. Significantly, five units were installed at NASA's Real Time Computer Complex to support the Apollo mission.
Models
Three distinct versions of the Model 75 were available: H75, I75, and J75. These models differed by the number of IBM 2365 Model 3 Processor Storage modules they contained—one for the H75, two for the I75, and four for the J75. Each storage module offered 262,144 bytes (256K) of core memory, translating into total memory sizes of 256K for the H75, 512K for the I75, and 1 megabyte for the J75.
Performance
The Model 75 delivered superior processing speeds through technologies such as parallel arithmetic operations, overlapped memory fetching, and simultaneous address computations. Its memory architecture featured independently accessible storage units that allowed two-way interleaving in the H75 and four-way interleaving in both I75 and J75 models. This design enabled an effective sequential access time as fast as 400 nanoseconds per double word (eight bytes) even with only two-way interleaving.
Features
Supporting the complete System/360 "universal instruction set" architecture, the Model 75 came equipped with standard capabilities for floating-point calculations, decimal processing, and character handling operations.