Acorn Archimedes 440

The 400 series included 4 expansion slots (although a 4 slot backplane could be added to the 300 series) and an ST506 controller for an internal hard drive. Both models included the Arthur OS (later called RISC OS), BBC BASIC and an emulator for Acorn's earlier BBC Micro, and were mounted in two-part cases with a small central unit, monitor on top, and a separate keyboard and three-button mouse.