Quite right, the gaps do not matter. The Omnibus is more of a typical computer bus than the Unibus which is more of an i/o bus. Kevin -----Original Message----- From: owner-classiccmp(a)classiccmp.org [mailto:owner-classiccmp@classiccmp.org]On Behalf Of Pete Turnbull Sent: 20 November 2001 08:31 To: classiccmp(a)classiccmp.org Subject: PDP-8 backplane -- was Re: PDP-8 case On Nov 20, 0:53, Tony Duell wrote: That reminds me... supplementary question: The machine had gaps between some of the cards. It's over 20 years since I used a PDP-8 for real, and in those days I wasn't usually allowed at the innards. The gaps don't matter, do they? There's no grant chain like in a Unibus, AFAIR. The -8/E is an Omnibus machine, of course. -- Pete Peter Turnbull Network Manager University of York