The Acorn A5000
The Acorn A5000 was released after the R260 but before the A3010, A3020, and the A4000, making the numbering rather odd. Where the A3010, A3020, and A4000 used the ARM250 system-on-chip, the A5000 still used discrete components and was powered by the ARM3CPU at 25MHz. The machine came with 1, 2, 4 or 8MByte of RAM, and a 20 up to 160MByte IDE hard drive.
Acorn Archimedes Computers
The Acorn Archimedes computer was the commercially available computer to use the RISC (Reduced Instruction Set CPU) architecture. The first models were launched in 1987, and Acorn developed updated models of the machines until the early 1990's. The CPU in the Acorn machines is the ARM chip, which stands for Acorn RISC Machine. ARM Chips are still used today, one popular example is the iPhone.
Arthur Operating System
The Acorn Archimedes computers were initially shipped with the Arthur OS, but could be upgraded to RISC OS, by replacing the ROM chips that contained the operating system. Because of these ROMs, the computer would boot immediatly into it's GUI, similar to the Atari ST line of computers. This gave them a significant advantage over PC's that loaded the operating system from disk.
The early Archimedes computers used the Arthur operating system, which was replaced in 1989 with RISC OS. RISC-OS featured co-operative multitasking, task management, solid window manipulation, adaptive rendering of bitmaps and coloring, and above all stability that the Arthur OS lacked. New applications quickly started to take advantage of the RISC-OS resulting in mature software such as Acorn Desktop Publisher, and even a PC Emulator.