Date: Wed, 30 Jan 2002 08:08:46 -0700 (MST) From: Ronald G Minnich <rminnich@lanl.gov> To: <babkin@FreeBSD.ORG> Cc: <hackers@FreeBSD.ORG>, <justin@mac.com> Subject: Re: OS Textbook FreeBSD Appendix Message-ID: <Pine.LNX.4.33.0201300804140.7168-100000@xed.acl.lanl.gov> In-Reply-To: <200201300214.g0U2E3f62586@freefall.freebsd.org>
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On Tue, 29 Jan 2002 babkin@FreeBSD.ORG wrote: > As far as I remember from reading the Lyons' book, there were > 16 mapping descriptors for text and data each. I think, 1/16 > of the address space is not too big, and in absolute values > it's the size of today's pages (4KB). well I had dropped this thread as I figured the list would not want to hear it, but yes you're right. The KT-11 MMU worked this way. I still have my manuals, as it was a pretty interesting piece of hardware. Unix was the first OS to actually use the split I/D capability, so while the various DEC OSes were stuck at 64K Unix programs could run at 64kI/64kD. Also user mode/super mode/kernel mode each got its own set. There was also a weird instruction called MFPU (move from previous user space) that allowed "bcopy shared memory"-type programming. Once again Unix actually used this, the DEC OSes did not, so Unix was the first to find the bugs in this hardware too. Once university as I recall actually added the wire to its machine to make MFPU work correctly ... The kinds of things you had to do in Unix on an 18-bit-physical address space machine with 16-bit addressing bear interesting similarities to what we have to do now on 36-bit mode Pentiums with 32-bit addresses. What goes around comes around ... ron To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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