Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: "Stephen Fuld" Newsgroups: comp.arch Subject: Re: interative use, The Design of Design Date: Thu, 9 May 2024 05:08:44 -0000 (UTC) Organization: A noiseless patient Spider Lines: 43 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Injection-Date: Thu, 09 May 2024 07:08:44 +0200 (CEST) Injection-Info: dont-email.me; posting-host="8e805b391587dfc38a6b74b1cfc52567"; logging-data="512856"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19H1UzlKRrwkFiprImNGySIjP2QhudZDRY=" User-Agent: XanaNews/1.21-f3fb89f (x86; Portable ISpell) Cancel-Lock: sha1:ZybT0ZT2yLPcvH3umlc1nUIQg0s= Bytes: 2890 John Levine wrote: > According to Stephen Fuld : > >> With sufficiently disciplined programming, you could swap and move > data >> by updating the base registers. APL\360 did this quite > successfully >> and handled a lot of interactive users on a 360/50. > > > > Wasn't APL\360 an interpreter? If so, then moving instructions and > > data around was considerably simpler. > > That's right. It could switch between users at well defined points > that made it practical to update the base registers pointing to the > user's workspace. > > >> Reading between the lines in the IBMSJ architecture paper, I get > the >> impression they believed that moving code and data with base > registers >> would be a lot easier than it was, and missed the facts > that a lot of >> pointers are stored in memory, and it is hard to > know what registers >> are being used as base registers when. > > > > Interesting. That would seem to imply that it wasn't that they > > didn't think about the problems that base addressing would cause, > > they just (vastly) underestimated the cost of fixing it. A > > different "design" problem indeed. > > In Design of Design, Brooks said they knew about virtual memory but > thought it was too expensive, which he also says was a mistake, soon > fixed in S/370. While I agree that virtual memory was probably too expensive in the mid 1960s, I disagree that it was required, or even the optimal solution back then. A better solution would have been to have a small number of "base registers" that were not part of the user set, but could be reloaded by the OS whenever a program needed to be swapped in to a different address than it was swapped out to. -- - Stephen Fuld (e-mail address disguised to prevent spam)