Risc PC | 1994
Risc PC
The Risc PC was a series of personal computers launched in 1994 by Acorn, replacing the Archimedes series. These machines used Acorn’s own ARM CPU and were not IBM PC-compatible.
At launch, the original Risc PC 600 model was equipped with an ARM 610, a 32-bit RISC CPU with 4KB of cache and clocked at 30MHz. However, CPU technology advanced rapidly, and within just two years, a DEC StrongARM CPU could be installed at 233MHz, offering performance around 8 times faster.
The Risc PC ran the RISC OS operating system, which had a windowed cooperative multitasking design. Unusually for a PC of the time, the operating system was stored in ROM, allowing for a relatively fast boot time.
In contrast to most contemporary IBM clones, the Risc PC supported multiple processors as a standard feature. The secondary, or "guest," CPUs did not need to be ARM-based and could be entirely different architectures. By adding an x86 CPU, it was possible to run operating systems like DOS and Windows 95. Other machines of the era often required an entire IBM PC clone card to run DOS software, but the Risc PC only needed the relevant CPU and some interface logic.
The Risc PC allowed alternate operating systems to run concurrently within a window. Applications from both operating systems could be run at the same time, sharing data between them, much like a virtual machine. This was a rare feature for PCs in 1994.
The Risc PC had a novel case design, where additional chassis units, called "slices," could be stacked on top of each other to expand the height of the machine. Up to six additional slices could be stacked, each containing extra drives or expansion cards (known as "podules"). Unlike the PCI bus standard used in the IBM clone industry, Acorn used its own bus implementation that was incompatible with the industry standard and required custom expansion cards. However, the Risc PC did use industry-standard IDE or SCSI drives.
Acorn discontinued production of the Risc PC in 1998 following a corporate reorganization, but Castle Technology continued manufacturing the machines until 2003, after which they produced their own similar designs. RISC OS is still available as an open-source product.
Technical Specifications:
CPU: Dual-processor slots, one host processor and one guest processor
- Host processors: ARM610 at 30MHz or 33MHz, ARM710 at 40MHz, StrongARM at 203MHz, 236MHz, 300MHz
- Guest processors: 486-class and at least IBM 5x86C processors up to 133MHz
- DSP chips (third-party) also available.
Memory: Two 72-pin FPM SIMM slots, supporting a maximum of 256MB.
Video Subsystem: VIDC20 controller with optional dual-port VRAM up to 2MB.
Expansion: Eurocard-sized podule support, with DMA support for the first two podule slots.
Operating System: RISC OS, stored in 4MB ROM (RISC OS 3.50 shipped on 2MB ROM)
- Pre-installed operating systems:
- RISC OS 3.50 (Risc PC 600)
- RISC OS 3.60 (Risc PC 700)
- RISC OS 3.70 (StrongARM Risc PC)
- RISC OS 3.71 (StrongARM Risc PC J233)
- RISC OS 4.03 (Kinetic Risc PC)
- RISC OS 4, RISC OS Select, RISC OS Adjust, RISC OS 6 available from RISCOS Ltd.
- RISC OS 5 from RISC OS Open (32-bit mode)
Case: Custom plastic-based design by Allen Boothroyd (designer of the BBC Micro case), featuring a "slice" system to expand the internal space.
Ports: RS-232 serial, parallel, PS/2 keyboard, Acorn mouse, headphone audio out, DE15 VGA, network (optional).
The Risc PC was used by music composers and scorewriters to run the Sibelius scorewriting software. Between 1994 and 2008, the Risc PC and A7000+ were used by OmniBus Systems for broadcast automation, and were at one point used in all national news broadcasts in the UK. OmniBus products were in use worldwide at nearly 100 broadcasters, including the BBC and ITN.
