Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!rutgers!mit-eddie!genrad!decvax!ucbvax!cbatt!ihnp4!alberta!bjorn From: bjorn@alberta.UUCP (Bjorn R. Bjornsson) Newsgroups: comp.arch Subject: Re: Architecture upgrade Message-ID: <166@pembina.alberta.UUCP> Date: Mon, 22-Dec-86 23:06:14 EST Article-I.D.: pembina.166 Posted: Mon Dec 22 23:06:14 1986 Date-Received: Tue, 23-Dec-86 22:36:16 EST References: <112@bnr-vpa.UUCP> <9200002@rmi.UUCP> <193@drilex.UUCP> <653@instable.UUCP> Organization: U. of Alberta, Edmonton, AB Lines: 48 Summary: The brilliance of the VAX design team, was expediency! In article <653@instable.UUCP>, amos@instable.UUCP (Amos Shapir) writes: > In article <7426@utzoo.UUCP> henry@utzoo.UUCP (Henry Spencer) writes: > >Remember when a 780's > >official designation was a "VAX-11/780"? > > Actually, DEC had made a brilliant (may be unintentional) upgrade, It could have been brilliant, but was greatly marred by flaws like the following: RTI and RTT ignore the mode bits in the PSW image on the stack, and set the mode to user without trapping. If RTI / RTT had trapped mode changes, or simply been left unimplemented, you could have written or ported real PDP-11 operating systems to run on the VAX. As it turned out, the AME (pseudo RSX-11M on a VAX), was useless except for trivial RSX applications, this because they left out socalled PLAS directives. What it did do was allow DEC to push the VAX through the door without any software. My suspicion has always been that DEC included compatibility mode in the early VAXen for this reason and this reason only. After the fashion of computer manufacturers, you then proceed advertise it as a feature. When you take it away, you can again advertise that as a feature, this time saying it's not taking up any resources, and users don't have to pay for something they don't need or want. Remember VMS versions 1 through 2. Almost utilities and compilers ran in compatibility mode. Yeah, DCL translated COPY commands to RSX PIP invocations, ditto for RENAME, DELETE, ad nauseum. The Fortran compiler was a modestly hacked version of PDP-11 Fortran-IV-Plus, and on and on and on. After version 2, more and more things started showing up in native mode. Until finally DEC was in a position to release VAXen without a PDP-11 mode, which is basically when they turfed it. It's easy to imagine that DEC would have been at least a year later in introducing the VAX without compatibility mode. Makes you wonder what the world would look like today, if that had been the case. Don't ascribe to brilliance, that which can be explained by simple expediency, Bjorn R. Bjornsson alberta!bjorn