Acorn Business Computers was committed to supporting multiple processors and architectures. For example, adding a Z80 to support CP/M.

However, financially it was not a success and Olivetti eventually took over a part in 1985.

At that time, Acorn only had the 8-bit computer line, while there were 16 and 32-bit computers on the market. At the end of 1985, Acorn introduced a new processor, a so-called RISC-cpu. This gave Olivetti enough confidence to refinance.

In June 1987, the first affordable computer with an RISC processor was launched on the market. The processor was the Acorn RISC Machine, abbreviated ARM.

There were 3 models released. The A305, A310 and A440. The A440 has expansion slots and an internal hard disk controller. The A305 and A310 did not have this standard, but could be expanded. The A305 has 512K memory as standard, the A310 has 1 MB and the A440 no less than 4 MB.

The operating system was completely new and was called Arthur (later RISC OS) and BBC Basic is also present in the system. It is a full 32-bit system capable of displaying 256 colors and 8-channel 8-bit sound.

The operating system is in ROM, which makes the computer start up very quickly, but upgrades can only be performed by swapping the ROM.

In 1989 the A300 series was succeeded by the Acorn Archimedes A3000