No, it doesn't. The order of CSR's doesn't have any bearing with what cards go where in the backplane. The order of cards in the backplane will depend on interrupt and DMA priority. Generally, peripherals that *will* lose data if they can't get serviced in time get put closest to the CPU. Examples here are serial lines, etc. Next come peripherals that will have to do a retry if they don't get serviced in time, but they will be able to do a retry. Tape drives, for example, might come here. Finally come devices where there's no real penalty for a retry, and maybe the peripheral doesn't care at all if the CPU takes its own sweet time in dealing with it. Something like a real-time clock would come in this category. What you're seeing there are the CSR autoconfigure rules in action. They're largely historical; the DZV11 is based on the DZ11, which is an "old-time" async multiplexer, and comes early in the autoconfigure rules. The DHV11 came many years later, and comes much later in the autoconfigure rules. If you're interested in knowing where the autoconfigure rules come from and how they're applied, take a look at Alan Frisbie's DECUS presentation at http://metalab.unc.edu/pub/academic/computer-science/history/pdp-11/hardwar… -- Tim Shoppa Email: shoppa(a)trailing-edge.com Trailing Edge Technology WWW: http://www.trailing-edge.com/ 7328 Bradley Blvd Voice: 301-767-5917 Bethesda, MD, USA 20817 Fax: 301-767-5927