The Acorn Archimeds A440 was the big brother to the A420 model, with even more memory, this machine came with 4MByte of memory, the same ARM2 RISC CPU running at 8MHz, and the upgraded backplane over the 300 series.

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.

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.

ARM, an acronym for Advanced RISC Machines (originally Acorn RISC Machines) is a Reduced Instruction Set Computer (RISC) cpu architecture. The ARM1, uses a 32-bit internal structure, but only had a 26-bit address space, limiting the processor to 64MByte of memory. This limit was removed in the ARMv3 series, which introduced a full 32-bit address space.

The first machine that used the ARM chip was the BBC Micro, it used the ARM as a secondary processor at 6MHz.

The result of the simulations on the ARM1 boards led to the late 1986 introduction of the ARM2 design running at 8 MHz, and the early 1987 speed-bumped version at 10 to 12 MHz. The ARM2 was roughly seven times the performance of a typical 7 MHz 68000-based system and twice as fast as an Intel 80386 running at 16 MHz.

The ARM2 featured a 32-bit data bus, 26-bit address space and 27 32-bit registers, of which 16 are accessible at any one time (including the Program Counter). The ARM2 had a transistor count of just 30,000, compared to Motorola's 68000 model with around 68,000. This simplicity enabled the ARM2 to have low power consumption, yet offer better performance than the Intel 80286.

A successor, ARM3, was produced with a 4 KB cache, which further improved performance. The address bus was extended to 32 bits in the ARM3.