Risc PC

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Risc PC

Acorn Risc PC 600 with two case slices, 3.5-inch disk drive and DVD-ROM drive
Developer	Acorn Computers
Manufacturer	Acorn Computers, Castle Technology[1]
Release date	15 April 1994; 30 years ago (1994-04-15)
Discontinued	11 November 2003 (2003-11-11)[2]
Operating system	RISC OS
CPU	ARMv3/ARMv4
Graphics	VIDC20
Dimensions	117 mm (4.6 in) (h) 355 mm (14.0 in) (w) 384 mm (15.1 in) (d)
Predecessor	Archimedes series
Successor	Phoebe, Iyonix PC, A9home
Related	A7000

Risc PC was a range of personal computers launched in 1994 by Acorn and replaced the preceding Archimedes series. The machines had a unique architecture unrelated to IBM PC clones and were notable for using the Acorn developed ARM CPU which is now widely used in mobile devices.^[3][4]

At launch, the original Risc PC 600 model was fitted as standard with an ARM 610, a 32-bit RISC CPU with 4KB of cache and clocked at 30MHz. CPU technology advanced rapidly in this period though and within only two years a DEC StrongARM could be installed at 233MHz which was around 8 times faster.^[5]

The machines ran the RISC OS operating system which has a windowed cooperative multi-tasking design. Unusually for a PC of the period the O/S was stored in ROM, which enabled a relatively fast boot time.

In contrast to most contemporary IBM clones, the machines supported multiple processors as a standard feature. Secondary (or "guest") CPUs did not need to be ARM based and could be an entirely different architecture. It was possible to add an x86 CPU which enabled use of operating systems including DOS and Windows 95. Cards could often be added to other machines of the era to run DOS software but more usually these would implement the majority of an IBM PC clone on the card. The Risc PC required only the addition of the relevant CPU with some interface logic.

Alternate operating systems ran concurrently with RISC OS in a window. Applications from both operating systems could run at the same time in a similar fashion to a virtual machine with data shared between them. While now a ubiquitous technology, this was a less common feature in 1994 and more usually only one operating system would run at once on a single PC.

The Risc PC had a novel case design where additional chassis, known as "slices", could be stacked on top of each other, expanding the height of the machine. Up to six additional slices could be stacked, each containing additional drives or expansion cards (known as "podules"). At the time the IBM clone industry was standardised around the PCI bus, but Acorn used its own bus implementation that was not compatible and required its own unique expansion cards. The machines did use the then industry standard IDE or SCSI drives found in contemporary PCs.

Acorn discontinued production of the Risc PC in 1998 after a corporate reorganisation but Castle Technology continued manufacturing the machines until 2003 and subsequently then produced their own similar designs. RISC OS is still available after becoming an open source product.^[6]