The heritage of RISC OS as an evolution of the BBC Micro MOS is really clear, at the lower levels. Not just the excellent BASIC, but the service calls, vector i

The heritage of RISC OS as an evolution of the BBC Micro MOS is really clear, at the lower levels. Not just the excellent BASIC, but the service calls, vector indirection, VDU system, command line interface and so on. Even the relocatable modules, one of the main unifying concepts in RISC OS, were sort of based on the sideways ROMs from the 8-bit machine. How different it would all have been had the ARX project been successful, although it was an incredibly 'optimistic' design from all I've ever heard about it. RISC OS was a terrifically fun environment in which to learn programming. Of course it lacked lots of the fundamentals of 'proper' operating systems (memory protection, preemptive task switching, multiple users etc etc) but the compromises they made were cleverly chosen and lots of parts of the design were very elegant. The user interface was great and there was lots of other very sophisticated features that were ahead of their time, discussed elsewhere in these comments (outline fonts, vector graphics, fast native video compression/decompression, the list goes on). The operating system was very easy to extend, so it was easy and fun to write little utilities, and this led to a vibrant hobbyist/'freeware' scene as I suppose it was called in those days. The fact that the OS was all implemented in assembler was reflected in the API, and (coupled with the inherent pleasure of working with the ARM instruction set of those days) led to the majority of third party apps being written in assembler too, often with bits of the very efficient built-in BASIC to bind it all together. This made the whole user experience very fast and slick. The documentation was also superb, though expensive for a youngster! I can't bring myself to get rid of the Programmer's Reference Manuals as they're so good and were such a holy text back in the day.