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Path: utzoo!watmath!watnot!ccplumb
From: ccplumb@watnot.UUCP (Colin Plumb)
Newsgroups: net.arch,net.periphs
Subject: Re: Why optical disks are slow to seek; an idea for higher capacity disks
Message-ID: <12152@watnot.UUCP>
Date: Tue, 4-Nov-86 22:17:58 EST
Article-I.D.: watnot.12152
Posted: Tue Nov  4 22:17:58 1986
Date-Received: Wed, 5-Nov-86 06:32:41 EST
References: <1128@tekig5.UUCP> <5100141@ccvaxa> <amdcad.13214> <553@cubsvax.UUCP> <2474@peora.UUCP> <1256@hoptoad.uucp>
Reply-To: ccplumb@watnot.UUCP (Colin Plumb)
Organization: U of Waterloo, Ontario
Lines: 34
Xref: watmath net.arch:4186 net.periphs:1275
Summary: 

In article <1256@hoptoad.uucp> gnu@hoptoad.uucp (John Gilmore) writes:
>
>I don't understand why nobody has built magnetic disks that spin at
>a constant speed, but vary the clocking of data to the disk so that
>all the bits end up the same width on the media.  This means that you
>might get 30,000 bytes per track on the inside and 90,000 on the 
>outside -- but who cares?  On a SCSI interface, the system doesn't know
>where the tracks and cylinders are anyway.
>
>I don't know how to figure it out exactly, but I suspect that this
>simple change (to a disk and its controller) could double the amount of
>stuff you could put on the same disk with the same heads and almost the
>same electronics.
>-- 
>John Gilmore  {sun,ptsfa,lll-crg,ihnp4}!hoptoad!gnu   jgilmore@lll-crg.arpa
>terrorist, cryptography, DES, drugs, cipher, secret, decode, NSA, CIA, NRO.
> The above is food for the NSA line eater.  Add it to your .signature and
> you too can help overflow the NSA's ability to scan all traffic going in or
> out of the USA looking for "significant" words.  (This is not a joke, sadly.)

They didn't carry it as far as possible, but Commodore varied the clock rates
on their 5-1/4" drives for the PETs and C-64s.  The difference was, I believe,
between 17 sectors on the inner tracks and 21 on the outer ones (don't quote me
on those figures).

You could do the same thing on an optical disk, since data-storage applications 
don't require constant bit-rates, the way real-time audio output does.

Is there an expert out there who could shed more light on the subject?

              -Colin Plumb (ccplumb@watnot.UUCP)

"You do have one slim chance for survival. This illness is so fatal it's been
 known to kill itself by accident."  -Sillier than Silly