Xref: utzoo unix-pc.general:753 comp.sys.att:3377 Path: utzoo!utgpu!water!watmath!uunet!lll-winken!lll-lcc!ames!ucsd!ucsdhub!jack!elgar!ford From: ford@elgar.UUCP (Ford Prefect ) Newsgroups: unix-pc.general,comp.sys.att Subject: Re: UNIXpc per-process VM limit (Was: Re: Swapping and wmgr) Message-ID: <167@elgar.UUCP> Date: 1 Jun 88 05:47:26 GMT References: <3030@crash.cts.com> <365@manta.UUCP> Reply-To: ford@elgar.UUCP (Ford Prefect ) Organization: Omnicron Data Systems, Bonita, CA Lines: 31 In article <365@manta.UUCP> brant@manta.UUCP (Brant Cheikes) writes: >In article <3030@crash.cts.com> ford@crash.CTS.COM (Michael Ditto) writes: >>The Unix PC supports 4M of virtual memory PER PROCESS, with a total amount >>dependant on your physical memory + swap space. > >I would like to see this claim substantiated. On page 2-1 of the AT&T >UNIXpc Interface Specification ("Detailed Interface Specification") >for version 3.51, it says: > > "Minimum real memory is 512K [...] and maximum process > size for a virtual memory program is 2.5 megabytes." > >Who's correct, the FM or Mr. Ditto? The manual is more accurate than I was. What I meant to say was that the Unix PC has 4 megabytes of virtual address space per process. 2.5M of that is usable for what most of us think of as "program" memory. The rest is shared library, shared memory, and reserved kernel space (bogus design tradeoff). What I mean by 4 megabytes of virtual address space is that the bottom 22 address lines (including the imaginary A0) coming off the CPU are decoded for user programs and converted into a physical memory location. Actually, all 24 address bits are decoded, but only the kernel is allowed to set the top two. -=] Ford [=- "Once there were parking lots, (In Real Life: Mike Ditto) now it's a peaceful oasis. ford%kenobi@crash.CTS.COM This was a Pizza Hut, ...!sdcsvax!crash!kenobi!ford now it's all covered with daisies." -- Talking Heads