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From: rbt@sftig.UUCP (R.Thomas)
Newsgroups: net.micro
Subject: Re: CD-ROMS
Message-ID: <550@sftig.UUCP>
Date: Tue, 16-Jul-85 14:13:05 EDT
Article-I.D.: sftig.550
Posted: Tue Jul 16 14:13:05 1985
Date-Received: Thu, 18-Jul-85 04:26:25 EDT
References: <11467@brl-tgr.ARPA>
Organization: AT&T Bell Laboratories, Summit, NJ
Lines: 35

> I would tend to doubt the practicality of "Unix on compact disks," at least
> as other than a distribution medium.  CD-ROM players are fairly slow in 
> the access time department, having a typical average seek time of 2 to
> 4 seconds in most cases.  The transfer rate isn't spectacular either,
> but not too bad.
>
> ...
>
>                                                     The players really
> aren't made for that sort of thing, and the basic parameters would
> be difficult to change.
> 
> By the way, I know of what I speak--I'm working with CD-ROMs right
> now; I have an official SONY CD-ROM test disc sitting not five
> feet away from me.  Sounds interesting in audio players, by the way...
> 
> --Lauren--

Not to contradict (least of all --Lauren--, whos information has always
been accurate as far as I can tell) but why are the basic parameters
difficult to change?  The main thing that is causing the 2-4 second average
seek time is the head movement time.  The disks spin at several hundred rpm
(I forget the exact numbers, but even 100 rpm would be only 0.3 sec average
rotational latency.)  The bit-rate is determined by the rotational speed,
so speeding up the head positioning should not affect the external
interface characteristics.  As I see it, the reason CDroms are slow is that 
they were designed for use in audio equipment, where head movement does not
need to be fast.  It ought to be possible to design a fast CDrom player for
computer use.  And somebody will, as soon as a mass market is demonstrated
to exist.  At first, the fast ones will be very expensive (relative to the
slow ones based on audio technology) because they will not be produced
in quantity.  But as they catch on, prices will come down as volumes go up.

Rick Thomas
ihnp4!attunix!rbt