High speed compact digital computer system

The ALU of a stored program computer comprises a plurality of 4- bit wide bit slices 400 and provides the addresses for fetching successive instructions from the main memory. In order to speed operation by prefetching instructions, two registers of 16 RAM registers 402 of the ALU bit slice 400 are dedicated to storing the current program count (CPC) and the next program count (NPC). Selectors 404 and 410 enable either such register to provide an address on the ALUOUT bus Y0-Y3. The two registers alternate their functions: CPC is incremented or jumped to become the new NPC while the old NPC becomes CPC.