Path: ...!news.mixmin.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Thomas Koenig Newsgroups: comp.arch Subject: Re: Address bits again, Article on new mainframe use Date: Mon, 2 Sep 2024 10:46:36 -0000 (UTC) Organization: A noiseless patient Spider Lines: 38 Message-ID: References: <2377cad7ee947ad71c9c3a8afbcdc26e@www.novabbs.org> Injection-Date: Mon, 02 Sep 2024 12:46:37 +0200 (CEST) Injection-Info: dont-email.me; posting-host="8931b5407bde990b59eec3041f2a60a5"; logging-data="2962005"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19zQDWbHvwksvuKx2usIlh9TUcDx8mppKg=" User-Agent: slrn/1.0.3 (Linux) Cancel-Lock: sha1:RMmgQanqnvgEbVSbcNAZr8vmdWY= Bytes: 2697 John Levine schrieb: > It is true that the -11 died for lack of address space, but nobody I > know has ever come up with a good design where the address size is > bigger than the word size. You end up with segments as on the 286 > or bank switching which is what later -11's did. What about the 6502? That was very much a 8-bit CPU, but cleverly used its zero page as index registers. Or all the other 8-bit CPUs, which usually had 16-bit address registers. People could have built CPUs with 16-bit accumulators and 32-bit addresses (or 8-bit accumulators and 32-bit addresses). It is debatable if these would have counted as a good design, though. > VAX stood for Virtual Address Extension. The key improvement was the > 32 bit addresses. Everything else was a detail. Some of those details > were unfortunate but that's a different argument. > > Also don't forget that back in that era everyone who had disks used > overlays. The IBM mainframe linkers had complicated ways to build > overlays and squeeze programs into 64K or whatever. Overuse of overlays almost sank OS/360. Brooks recounts that, on a high-end machine, the FORTRAN compiler would have compiled only a few lines per minute. It was caught in time by simulation. But the MVS linker was slooooooooooow. I remember waiting for fifteen to 30 minutes of wall time for a link step to complete, on a much later model. > Even though the > address space was 16MB it was a long time before machines had that much > RAM and by then they'd added paging to make the physical memory size less > relevant. Browsing through Wikipedia, it seems the biggest memory on a /360 was 6 MB.