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
<http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/geom.html>
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.
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