 It comprised a power supply, interface logic and a connector that matched the internal co-processor connector built into the BBC Master main board.This allowed the BBC B and B+ to use the Turbo board (4 MHz 65C102 with 64 KB of RAM) and the Master 512 board (10 MHz 80186 with 512 kKB of RAM), by fitting them into this expansion unit.It also allowed the BBC Master to have two internal co-processor boards connected, only one of which could be enabled through software.