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From: phil@brahms.amd.com (Phil Ngai)
Newsgroups: comp.arch
Subject: Re: CD-ROM documents (was Paperless Office)
Message-ID: <1990Dec10.185611.19343@amd.com>
Date: 10 Dec 90 18:56:11 GMT
References: <1990Dec5.105743.25693@actrix.gen.nz> <1990Dec6.154348.5206@d.cs.okstate.edu> <1990Dec7.020857.18469@amd.com> <1990Dec8.174708.2391@bilver.uucp>
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bill@bilver.uucp (Bill Vermillion) writes:

>Except the big difference in the magnetic media is there are many tracks,
>with a high tpi density.  In a CD-ROM there is essentialy ONE track, which
>is a spiral.

Primarily, I was responding to the claim that CD-ROMs are inherently
slow because the use of Constant Linear Velocity forces a change in
RPM when seeking. I agree that finding the track is a little more difficult
on CD-ROMs than on magnetic media but the big bottleneck for seeks right
now seems to be the rotational inertia of the disk, which could be
bypassed if the methods used in magnetic media for accomodating varying
bit rates were adopted.

>In magnetic media you can say at track xx we will go to an xxxx bit rate
>and when we reach track yy we can go to a yyyy bit rate.

Simple physics tells you what the bit rate at radius X will be approximately.

>In CDs the tracks are independant of the drives.  And if you examine the
>specifications for CD mastering you will find that there is a range for
>spacing the "tracks".   Therefore you can not position a CD-ROM the same

Then perhaps as part of the startup process the drive could determine
the "track" spacing, assuming that it is relatively constant on a
particular disk and varies from disk to disk only because of different
data lengths.

--
There is no right more fundamental than self-defense.