From owner-freebsd-hackers@FreeBSD.ORG Sat Dec 29 17:39:20 2007 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id D368D16A417 for ; Sat, 29 Dec 2007 17:39:20 +0000 (UTC) (envelope-from mwm-keyword-freebsdhackers2.e313df@mired.org) Received: from mired.org (bhuda.mired.org [66.92.153.74]) by mx1.freebsd.org (Postfix) with SMTP id 6BE1A13C4D3 for ; Sat, 29 Dec 2007 17:39:20 +0000 (UTC) (envelope-from mwm-keyword-freebsdhackers2.e313df@mired.org) Received: (qmail 29797 invoked by uid 1001); 29 Dec 2007 17:39:11 -0000 Received: from bhuda.mired.org (localhost.localdomain [127.0.0.1]) by bhuda.mired.org (tmda-ofmipd) with ESMTP; Sat, 29 Dec 2007 12:39:11 -0500 Date: Sat, 29 Dec 2007 12:39:10 -0500 To: freebsd-hackers@freebsd.org Message-ID: <20071229123910.3ed3c68b@bhuda.mired.org> In-Reply-To: <20071229124120.GA23415@owl.midgard.homeip.net> References: <47760132.5040306@pacific.net.sg> <47761B63.4010407@pacific.net.sg> <20071229124120.GA23415@owl.midgard.homeip.net> Organization: Meyer Consulting X-Mailer: Claws Mail 2.9.1 (GTK+ 2.10.12; amd64-portbld-freebsd6.2) Face: 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 Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Delivery-Agent: TMDA/1.1.11 (Ladyburn) From: Mike Meyer Subject: Re: Architectures with strict alignment? X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 29 Dec 2007 17:39:20 -0000 On Sat, 29 Dec 2007 13:41:21 +0100 Erik Trulsson wrote: > On Sat, Dec 29, 2007 at 06:03:15PM +0800, Erich Dollansky wrote: > > All RISC based designs need the alignment so that the CPU can fetch a CPU > > word in one go. CISC based designs do not have this limitiation. > > > > I also do not know of any other CISC based design which made it to > > mainstream. I think this would be more correctly expressed as "still survive in the mainstream." > Not quite true. Take for example the venerable Motorola 68000 CPU (used in > many different computers in the early and mid 80's). > It required all 16-bit (and 32-bit) accesses to be aligned on a 16-bit > boundary. This was later relaxed in the M68020 and later CPUs. The same is true of the IBM 360 architecture - had it initially, and dropped it in later revisions - which was at one time the most popular architecture in the world, complete with competitors cloning it to take advantage of the software base. FWIW, it was also the first architecture where it made sense to ask this question. Prior to the 360, computers were either business machines, and only did things with/to bytes, or they were scientific computers, and only did things with/to words. It's ability to both is one of the reasons it became the most popular architecture in the world, and that basic design now dominates the industry. http://www.mired.org/consulting.html Independent Network/Unix/Perforce consultant, email for more information.