Drums

From: Chuck McManis <cmcmanis_at_mcmanis.com>
Date: Tue Apr 18 12:36:20 2000

At 09:37 AM 4/18/00 -0700, Shawn wrote:
>Well the set of all the same-numbered tracks on a stack of hard drive
>platters also form a cylinder... I thought that was the reason.

My understanding of this, and I believe the source was Bill Joy when I was
over at Sun describing the Berkeley "Fast File System" is as follows:
Both John and Shawn are correct. The derivation of the term "cylinder" for
disk geometry descriptions came from the fact that in a multi-headed drive,
Track 'n' on all platters formed one cylinder. Given that disks had a hard
time seeking quickly, things that you could put on one cylinder could be
accessed like a drum without any head movement. In BSD they added "cylinder
groups" which were collections of cylinders (usually 3, sometimes 5) where
the heads need only move in our out one or two steps from the "home"
cylinder to get to a particular bit of data. Then by clustering data into
cylinder groups you could acheive higher disk throughput then if you put
things onto any old track.

--Chuck
Received on Tue Apr 18 2000 - 12:36:20 BST