Games - RISC OS

	Games - RISC OS

RISC OS, which stands for Reduced Instruction Set Computing Operating System is a British Graphical user interface-based operating system for ARM-processor based computers or similar devices. In certain countries (particularly the UK) it was an important operating-system before the dot-com computing era.

Early years (Arthur)

The OS was designed in England by Acorn for the 32-bit ARM based Acorn Archimedes, and released in its first version in 1987, as the Arthur operating system.

RISC OS 2

RISC OS was a rapid development of Arthur 1.2 after the failure of the ARX project. The first release was to be called Arthur 2, but was renamed to RISC OS 2, and was first sold as RISC OS 2.00 in April 1989. It had co-operative multitasking with some limitations, but was not multithreaded. It used the ADFS filesystem for both floppy and hard discs. It initially ran from a 512 KB ROM module. The WIMP interface offered all the standard features and fixed many of the bugs that had hindered Arthur. It lacked virtual memory and extensive memory protection (applications are protected from each other, but many functions have to be implemented as 'modules' which have full access to the memory). The main advantage of the OS was its ROM; it booted very quickly and while it was easy to crash it was impossible to break. Its high performance was due to much of system being written in ARM assembly language. The OS was organised as a relatively small kernel which defined a standard software interface to which extension modules were required to conform. Much of the system's functionality was implemented in modules coded in the ROM, though these could be supplanted by more evolved versions loaded into RAM. Among the kernel facilities were a general mechanism, named the callback handler, which allowed a supervisor module to perform process multiplexing. This facility was used by a module forming part of the standard editor program to provide a terminal emulator window for console applications. The same approach made it possible for advanced users to implement modules giving RISC OS the ability to do pre-emptive multitasking.

One unusual and innovative feature of the operating system at the time of its release was its support for high-quality, hinted and anti-aliased outline font rendering, a feature that only became widespread in other operating systems much later.

A slightly updated version RISC OS 2.01 was released later to support the ARM3 processor that was shipped with the Archimedes A540 and Acorn R225/R260.

RISC OS 3

RISC OS 3.00 was released with the A5000 in 1991; it was almost four times the size of RISC OS 2 and ran from a 2MB ROM. It improved multitasking and also placed some of the more popular base applications in the ROM.

RISC OS 3.1

RISC OS 3.1, was released later which was sold built-in to the A3010, A3020, A4000, A4 and later A5000 models. It was also made available as replacement ROMs for the A5000 and earlier Archimedes machines, this is the last version suitable for those machines. Three variants were released RISC OS 3.10 the base version, RISC OS 3.11 a slight update that fixed some serial port issues, and RISC OS 3.19 which was a German translation.

RISC OS 3.5

RISC OS 3.50 was sold from 1994 with the first Risc PCs. Due to the very different hardware architecure of the Risc PC, including an ARM 6 processor, 16 and 24 colour and a different IO chip, RISC OS 3.50 was not made available for the older Archimedes and A Series ARM 2 and 3 machines.

RISC OS 3.6

RISC OS 3.60 followed in 1995, the OS was updated and featured much better hard disk access and its networking was enhanced to include TCP/IP in addition to Acorn's existing proprietary Econet system. Also the hardware support was improved, Risc PCs could now use ARM 7 processors and Acorn's A7000 machine with its ARM 7500 processor was also supported.

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