From owner-freebsd-doc@FreeBSD.ORG Tue Feb 4 12:03:22 2014 Return-Path: Delivered-To: freebsd-doc@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 7E70E96B for ; Tue, 4 Feb 2014 12:03:22 +0000 (UTC) Received: from bs1.fjl.org.uk (bs1.fjl.org.uk [84.45.41.196]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.freebsd.org (Postfix) with ESMTPS id CBFBE14BB for ; Tue, 4 Feb 2014 12:03:21 +0000 (UTC) Received: from [192.168.1.35] (host86-161-164-213.range86-161.btcentralplus.com [86.161.164.213]) (authenticated bits=0) by bs1.fjl.org.uk (8.14.4/8.14.4) with ESMTP id s14C3J34028339 (version=TLSv1/SSLv3 cipher=DHE-DSS-CAMELLIA256-SHA bits=256 verify=NO) for ; Tue, 4 Feb 2014 12:03:20 GMT (envelope-from frank2@fjl.co.uk) Message-ID: <52F0D705.1090402@fjl.co.uk> Date: Tue, 04 Feb 2014 12:03:17 +0000 From: Frank Leonhardt User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: freebsd-doc@freebsd.org Subject: Re: GEOM meaning References: <52F0C512.8080909@online.de> <52F0D58F.4040703@fjl.co.uk> In-Reply-To: <52F0D58F.4040703@fjl.co.uk> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Content-Filtered-By: Mailman/MimeDel 2.1.17 X-BeenThere: freebsd-doc@freebsd.org X-Mailman-Version: 2.1.17 Precedence: list List-Id: Documentation project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 04 Feb 2014 12:03:22 -0000 On 04/02/2014 11:57, Frank Leonhardt wrote: > On 04/02/2014 10:46, Dieter Lange wrote: >> Hi, >> >> having looked at quite a few sites now, not just >> >> I still cannot find out what "GEOM" means (wrt disks etc., not >> geography or so). It probably does not mean "Modular Disk >> Transformation Framework". I am not talking of its use and/or >> definitions, just the meaning of the abbreviation or word... >> >> Thanks+kind regards from the only person on the WWW who doesn't know... >> DL > > I've always assumed it was short for (disk) geometry - i.e. converting > logical requests to match the disk geometry. Eh? Well, back in my > youth we did talk about the "geometr"y of DASD (disk!). For example, > how many platters (heads), cylinders (tracks) and sectors/track were > present. With ATA and SCSI this has become less relevant as you only > get to see the logical structure of a disk (a load of blocks > sequentially numbered 0...n). You may well ask why anyone would call > these parameters "geometry", but I can't think of any other better > name for it, nor any other word in common use for referring to them > (other than CHT). But a disk's geometry was highly relevant because > you (the programmer) would either be responsible for moving the head > (via a stepper motor) to the correct track, or at the very least, you > had to be sensitive to where the head was on the disk when optimising > your code. > > I've no proof whatsoever that this is why the geom library is so > called - it could all be a complete coincidence. I don't remember > hearing about "geom" on System V, nor on BSD until recently (late 1990s). > > Regards, Frank. > P.S. The reason why I'm not 100% happy with the above theory is that the geom library sits between DEVFS and the device driver (pretending to be a device driver to DEVFS). This doesn't seem to me the logical place for geometry translations, but it wouldn't be the first time a name has ended up migrating to another purpose.