The Acorn System 3A comprised:
pair of 8K RAM + 8K ROM Boards (populated with 16K RAM)
8-Slot Backplane (fully populated with 8 sockets and buffers for the address bus)
3U Cased Card Frame (with 8 sets of card guides, boards fitted with front panels)
Disk Operating System (DOS) in ROM
System BASIC in ROM
System BASIC Floating Point in ROM
Optional extras:
Monitor