Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!elroy!cit-vax!mangler
From: mangler@cit-vax.Caltech.Edu (Don Speck)
Newsgroups: comp.arch
Subject: Re: Disk drives -- speed of?
Message-ID: <6166@cit-vax.Caltech.Edu>
Date: 18 Apr 88 08:01:01 GMT
References: <2746@sundc.UUCP>
Organization: California Institute of Technology
Lines: 23
Summary: disk rotation rates

In article <2746@sundc.UUCP>, bwong@sundc.UUCP (Brian Wong) asks:
> why don't we see disks running faster than 3600 rpm?

Because that would increase the bit rate, and the controller's
can't handle it.  (It continually amazes me that the electronics
can't keep up with something that is electro-mechanical...)

The Fujitsu Eagle M2351 spins at 3961 rpm and transfers at 15 MHz,
which made it too fast for any of the controllers available when it
was introduced in the early 1980's.  Many later high-density disks
have instead opted to hold down the rotation rate so they could use
existing controllers.  The best example is the CDC 9771, which spins
at 2160 rpm (also available in a 3600-rpm version, the CDC 9772).

Rumor has it that Fujitsu's recent 8-inch disks have a jumper to make
them spin faster, but since even the normal transfer rate is at the
maximum of many controllers (20 MHz), this is of limited utility.
It's probably intended for places where the air is thin, to increase
the flying height.

What the disk industry needs most are a few good 40 MHz controllers.
SCSI and IPI show some promise in this area.

Don Speck   speck@vlsi.caltech.edu  {amdahl,ames!elroy}!cit-vax!speck