From owner-freebsd-hackers Wed Jan 30 7: 8:52 2002 Delivered-To: freebsd-hackers@freebsd.org Received: from acl.lanl.gov (acl.lanl.gov [128.165.147.1]) by hub.freebsd.org (Postfix) with SMTP id 465AB37B404 for ; Wed, 30 Jan 2002 07:08:47 -0800 (PST) Received: (qmail 775237 invoked from network); 30 Jan 2002 08:08:46 -0700 Received: from xed.acl.lanl.gov (128.165.147.191) by acl.lanl.gov with SMTP; 30 Jan 2002 08:08:46 -0700 Received: (qmail 7170 invoked by uid 3499); 30 Jan 2002 08:08:46 -0700 Received: from localhost (sendmail-bs@127.0.0.1) by localhost with SMTP; 30 Jan 2002 08:08:46 -0700 Date: Wed, 30 Jan 2002 08:08:46 -0700 (MST) From: Ronald G Minnich X-X-Sender: To: Cc: , Subject: Re: OS Textbook FreeBSD Appendix In-Reply-To: <200201300214.g0U2E3f62586@freefall.freebsd.org> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG 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