<> More recently, Intel designed the 8089 I/O co-processor as part <> of the 8086 family. It had an instruction set optimized for I/O <> functions. And not so recently starting with the AT and all after the keyboard interface chip is a slave cpu (8041a or 8042). In 81 I started a system using multiple z80s and 8085s to do things like disk IO and loosely coupled multiprocessing (using z80s). When I had it up and operational it could outrun a dos powered 386/20. Slave procesors and distributed cpus are not new. One favorite is the PDP-12, a PDP-8 with a linc-8 as a peripheral. The PDP-10 used PDP-8 as an IO processor or later ones used PDP-11s. Even the Microvax-II disk controller had a T-11(chip version of a base PDP-11). Allison