What it is and the problem it solves
The IBM System/360 is a family of mainframe computers announced on April 7, 1964. It solved the problem of vendor lock-in and software rewrite costs by enabling companies to upgrade hardware without rewriting applications.
How it works
It separated architecture from implementation, enabling compatible models at different price points. It used microcode (except in Model 44 and the most expensive systems) to implement an instruction set with 8-bit byte addressing and multiple arithmetic formats. It introduced Solid Logic Technology — discrete transistor-based circuit cards — deliberately excluding integrated circuits as immature.
What works
Application compatibility worked across most models. Performance scaled predictably: Model 30 delivered up to 34,500 instructions per second; Model 91 delivered up to 16.6 million. Memory configurations ranged from 8 KB to 8 MB, with common large installations using 512–1024 KB.
What does not
It did not use integrated circuits. It did not deliver full compatibility across all models: Model 44 was only partially compatible. It did not achieve uniform memory scaling: 8 MB was a theoretical maximum, rarely deployed; typical large installations used 256–1024 KB.
What it changes
It changed how computer families were conceived: no longer bespoke machines, but tiered, upgradeable systems sharing software. It established that application portability across performance tiers could be engineered — not assumed — through disciplined architecture/implementation separation.
Is it worth your time
Yes, if you work with legacy system design, compatibility trade-offs, or hardware abstraction. Its mechanism — architectural standardisation without silicon integration — remains a masterclass in pragmatic scalability. But its relevance is historical, not operational.