On May 5, 11:37, Daniel A. Seagraves wrote: It certainly would. Even the RT-11 driver (which is about the simplest I've seen) is fairly complex. It's basically a message-passing protocol, unlike most of the earlier DEC disk stuff where you can poke the hardware registers to "make things happen". To oversimplify, with MSCP you make a message containing instructions, put it in a memory buffer somewhere, tell the controller it's there, and it does the rest with DMA, returning a response message. The relevant documentation is "MSCP Basic Disk Functions Manual", AA-L619A-TK, and "Storage System Diagnostics And Utility Protocol", AA-L620A-TK, which in turn are parts of the UDA50 Programmer's Documentation Kit (QP-905-GZ). My copy is version 1.2, April 1982. It's not good bedtime reading; the plot's a bit too convoluted and the characterisation is weak :-) -- Pete Peter Turnbull Dept. of Computer Science [remove indy. from email address to reply] University of York