Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!husc6!babbage!reiter From: reiter@babbage.harvard.edu (Ehud Reiter) Newsgroups: comp.arch Subject: Re: In defense of the VAX Message-ID: <1226@husc6.harvard.edu> Date: 20 Feb 89 21:47:18 GMT References: <4592@tekgvs.LABS.TEK.COM> <638@m3.mfci.UUCP> <11037@tekecs.TEK.COM> <653@m3.mfci.UUCP> Sender: news@husc6.harvard.edu Reply-To: reiter@harvard.UUCP (Ehud Reiter) Organization: Aiken Computation Lab Harvard, Cambridge, MA Lines: 41 I still remember how happy I was when I was first introduced to the VAX, a decade or so ago, after too many years on PDP's, 370's, and Interdata machines. So, I can't resist the chance to make a few comments. The VAX represented the best archicture that could be done in the mid 70's. The computing situation was a bit different then, and in particular 1) Lots of code was written in assembler. This meant that machines had to have an assembly language that was easy for humans to use, which meant lots of addressing modes and data types, as much orthogonality as possible, and high-level instructions where possible. In short, if people were going to write lots of programs in assembler, then it was important to give them as powerful and high-level an assembler language as possible. 2) Memory was expensive. Remember the days when 15 people time-shared on a VAX with 1 MB of memory? Given this, dense coding of instructions made a lot of sense, particularly since dense coding probably helped performance of the 11/780 more than it hurt (it didn't hurt the pipeline, since the 780 wasn't pipelined, and it probably made the I-cache more effective and paging less common). In the late 1980's, the situation is a lot different. Assembly programming is much rarer, thanks to ever-better languages and compilers, and memory is so cheap that even PC's have several MB. One could even argue that the state of the art in computer architecture has improved, with more reliance on data and less on intuitive feelings. The newer architectures, like MIPS, are probably more appropriate for the 90's than the VAX - but's that progress. It would be somewhat disappointing if we hadn't progressed beyond the VAX in the last 10-15 years. And, note that people criticize the VAX architecture on performance, not functionality. The most important thing about an architecture is that it should make it easy for people to write and run programs, and I don't think anyone has complaints about the VAX on this score. This contrasts with the IBM 370-class machines, which suffer greatly from lack of address space, which *is* very much an annoyance to the programmer and even the end-user. Ehud Reiter reiter@harvard (ARPA,BITNET,UUCP) reiter@harvard.harvard.EDU (new ARPA)