From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lucio De Re To: 9fans@cse.psu.edu Subject: Re: [9fans] how people learn things (was architectures) Message-ID: <20010713182020.C22003@cackle.proxima.alt.za> References: <20010713091130.B8A0D199C0@mail.cse.psu.edu>, <20010713131151.Y22003@cackle.proxima.alt.za> <3B4F091E.9242B958@null.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <3B4F091E.9242B958@null.net>; from Douglas A. Gwyn on Fri, Jul 13, 2001 at 03:26:08PM +0000 Date: Fri, 13 Jul 2001 18:20:22 +0200 Topicbox-Message-UUID: ccc45d80-eac9-11e9-9e20-41e7f4b1d025 On Fri, Jul 13, 2001 at 03:26:08PM +0000, Douglas A. Gwyn wrote: > > Lucio De Re wrote: > > No more than from Intel (they are to be blamed for CP/M, too), > > overlooking the fact that their address bus was wider than the > > register size, or scrapping the i860/i960 developments. > > They are rushed decisions that can't be reversed. ... > > Even the original PDP-11 had a wider address bus than its > register (word) size. It wasn't a "rushed decision", although > in the long run it caused enough trouble that a whole new > architecture was designed to replace it. Do you mean to tell me that DEC had a segmented architecture, with haphazard default "base" registers, a LOCK instruction to lock the bus for the following fetch cycle (whatever for? even the Univac 1106 had the more sane test-and-set) and a faulty MOV SS,XX that did _not_ lock the bus for the following MOV SP,YY as was the intention? I bet the 20-bit address was an oversight, one that is still being dragged along in this era of 64-bit registers. For heaven's sake, Intel's marketing hype was full of praise for the ability to have 2^12 (overlapping) segments, and to this day the Pentium has segment registers. Worse, one reads of superservers addressing up to 64Gigabytes of main memory - must be programmed in assembler 'cause it's a long time since I've seen a compiler capable of producing segmented architecture code. > architecture was designed to replace it. No, not to "replace it", but to propagate it. ++L