Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!oliveb!Roma!lance From: lance@Roma.orc.olivetti.com (Lance Berc) Newsgroups: comp.unix.wizards Subject: Re: When did paging get into System V Message-ID: <21688@oliveb.olivetti.com> Date: 12 May 88 22:18:17 GMT References: <53@lazlo.UUCP> <142700033@occrsh.ATT.COM> <651@pyuxe.UUCP> <382@cloud9.UUCP> <7878@brl-smoke.ARPA> Sender: news@oliveb.olivetti.com Reply-To: lance@Roma.UUCP (Lance Berc) Organization: Olivetti Research Center, Menlo Park, CA Lines: 29 In article <7878@brl-smoke.ARPA> gwyn@brl.arpa (Doug Gwyn (VLD/VMB) ) writes: >(Sun >designed their original memory management hardware to look virtually >the same as the VAX's, to avoid this. Not everyone has had that option.) The memory hardware of Vaxen and Suns (at least twos and threes) are COMPLETELY different. The only similarity is that Sun-2s support separate control bits for RW(X?) for both user and supervisor, and that both have two levels of tables involved in virtual to physical address calculation. Sun-3s have only two protection bits: read/write and user/supervisor (just like the 80386...). Vaxen have both a real-mode (mapping disabled) and TLBs, Suns don't have either (all references go through the mapping hardware, which is fast enough to eliminate the need for a TLB, at least on Sun-2s). Vaxen have page tables in main memory, with pageable secondary page tables. Suns have mapping information in specially accessed fast memory, and have a cache of eight adress space `contexts'. If a Sun requires a ninth address space then an entire context description has to be swapped out. And to ice the cake, Suns even have Reference Bits! lance Lance M. Berc Phone: (415) 496-6248 Olivetti Research Center Internet: lance@orc.olivetti.com, or 2882 Sand Hill Road, Suite 210 lance%orc.uucp@unix.sri.com Menlo Park, CA 94025 UUCP: {acornrc,oliveb,sri-unix}!orc!lance