Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!mips!dimacs.rutgers.edu!aramis.rutgers.edu!paul.rutgers.edu!njin!spcvxb.spc.edu!terry From: terry@spcvxb.spc.edu (Terry Kennedy, Operations Mgr.) Newsgroups: comp.sys.dec Subject: Re: pdp-11's Message-ID: <1991Jun22.041102.1509@spcvxb.spc.edu> Date: 22 Jun 91 04:11:02 GMT References: Distribution: comp Organization: St. Peter's College, US Lines: 27 In article , rocker@bucsf.bu.edu (The Long Haired One) writes: > > These are probably a very simple questions. I just don't know the answers. > I noticed that Pdp11's come in 2 types - qbus and unibus. Do the numbers > of the machines like pdp-11/23 and pdp-11/24 relate to which is which type? Yup. In general, the 11/x3's are Q-bus: the 11-03/23/53/73/83/93 systems. Unibus model numbers wander all over the place 8-). There are also some sys- tems that are neither Unibus nor Q-bus; the PRO series comes to mind... > And can someone tell me the differences between qbus-ing and unibuses, as > to which is possibly better or what drawbacks they might hold. Q-bus is a somewhat newer system which uses multiplexed address and data lines; the Unibus has seperate address and data buses. There are also other differences, but that is the major technical one. Unibus systems tend to be larger and more power-hungry. Recent advances (in geological terms) such as block mode DMA and the PMI have made the Q-bus almost as fast as, and in many cases, faster than, the Unibus. DEC no longer makes Unibus VAXen; they still make Q-bus ones. PDP-11's are available in both configurations, although the current Unibus ones are actu- ally Q-bus systems with a Unibus adapter. Terry Kennedy Operations Manager, Academic Computing terry@spcvxa.bitnet St. Peter's College, US terry@spcvxa.spc.edu (201) 915-9381