From owner-freebsd-hackers Wed May 20 14:59:24 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id OAA07413 for freebsd-hackers-outgoing; Wed, 20 May 1998 14:59:24 -0700 (PDT) (envelope-from owner-freebsd-hackers@FreeBSD.ORG) Received: from gatekeeper.alcatel.com.au (gatekeeper.alcatel.com.au [203.17.66.1]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id OAA07126 for ; Wed, 20 May 1998 14:57:45 -0700 (PDT) (envelope-from peter.jeremy@alcatel.com.au) Received: from mfg1.cim.alcatel.com.au ("port 3637"@[139.188.23.1]) by gatekeeper.alcatel.com.au (PMDF V5.1-7 #U2695) with ESMTP id <01IXADLPSMW0000YPH@gatekeeper.alcatel.com.au> for hackers@FreeBSD.ORG; Thu, 21 May 1998 07:57:01 +1000 Received: from gsms01.alcatel.com.au by cim.alcatel.com.au (PMDF V5.1-10 #U2695) with ESMTP id <01IXADLO9SJKB51FAT@cim.alcatel.com.au> for hackers@FreeBSD.ORG; Thu, 21 May 1998 07:56:59 +1000 Received: (from jeremyp@localhost) by gsms01.alcatel.com.au (8.8.8/8.7.3) id HAA15942 for hackers@FreeBSD.ORG; Thu, 21 May 1998 07:56:58 +1000 (EST) Date: Thu, 21 May 1998 07:56:58 +1000 (EST) From: Peter Jeremy Subject: Intel vs the rest (was `Original PC' and `talk') To: hackers@FreeBSD.ORG Message-id: <199805202156.HAA15942@gsms01.alcatel.com.au> Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG On Wed, 20 May 1998 10:43:54 +0200 (CEST), Oliver Fromme wrote: >There was also an 68000-8 with external 8 bit bus. As I remember, the 68008 came out much later. The only thing I can think of that used it was the Sinclair QL - which was mid-80's. On Wed, 20 May 1998 10:42:12 +0100, Karl Pielorz wrote: >Is it me or is basically everyone here either a) Not a big fan of Intel >(strange considering what FreeBSD runs on ;-) Possibly as a result of having to work with the architecture :-) >b) Prefers the Motorola? (I certainly do!), and / or c) Largely used to own, >program, hack on Amiga's? - or at least want FreeBSD to work as well as the >Amiga did Agreed on all three. It's worth noting that Windoze-95 gave PC users the same capabilities that the Amiga had when it came out (PnP was part of the original Amiga spec). On Wed, 20 May 1998 19:58:48 +0930, Greg Lehey wrote: > but nowadays the register model isn't very important to >anybody except compiler writers. The register model _does_ directly affect performance (admittedly, only marginally). Also, the overall architecture has a substantial impact on the complexity/performance tradeoffs. The major effect is that having more registers means that local variables are less likely to spill onto the stack - where they'll be slower to access(*), result in larger code and may trigger further spills to provide work registers in the absence of orthoganal mem-mem instructions. (More registers also increase the instruction size, reducing code density where the registers aren't needed). As an example of the impact of an architectural decision on complexity: The 68k included a clear split between (non-modifiable) instructions and (modifiable) data, the x86 didn't (and early applications often used self-modifying code). This means that the x86 needs a unified cache, whilst the 68k uses a split cache - which gives it two immediate advantages: The I-cache is also somewhat simpler (no need for dirty bits or the write-{through,back} logic), allowing more of it for the same complexity. Dual caches allow parallel I and D accesses - ie effectively doubling the cache <-> CPU bandwidth (dual- porting the cache can be done, but entails a substantial increase in complexity). (The downside is that a unified cache will adjust to different code vs data footprints - giving somewhat better hit rates for a given total cache size). Have a look at the performance vs transistor counts for things like Chuck Moore's MuP21. (*) The stated instruction timings may be the same but when you account for all the caveats on memory accesses, it'll be slower in reality. Peter -- Peter Jeremy (VK2PJ) peter.jeremy@alcatel.com.au Alcatel Australia Limited 41 Mandible St Phone: +61 2 9690 5019 ALEXANDRIA NSW 2015 Fax: +61 2 9690 5247 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message