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From: drysdale@cbmvax.commodore.com (Scott Drysdale)
Newsgroups: comp.sys.amiga.emulations
Subject: Re: Question about Cross-Dos
Message-ID: <22358@cbmvax.commodore.com>
Date: 12 Jun 91 18:14:11 GMT
References: <1991Jun11.215637.563@wpi.WPI.EDU> <1991Jun12.001931.3711@ucselx.sdsu.edu> <507@regina.uregina.ca>
Reply-To: drysdale@cbmvax.commodore.com (Scott Drysdale)
Organization: Commodore, West Chester, PA
Lines: 64

In article <507@regina.uregina.ca> cazabon@hercules.uregina.ca (Charles Cazabon (186-003-526)) writes:
>In article <1991Jun12.001931.3711@ucselx.sdsu.edu> civir1070@ucsvax.sdsu.edu writes:
>:In article <1991Jun11.215637.563@wpi.WPI.EDU>, amartin@wpi.WPI.EDU (Allen R Martin) writes...
>:> 
>:>	Will Cross-Dos work with an AE high density drive to read IBM
>:>high density disks?  I don't see any reason why it shouldn't but I was 
>:>just wondering if anyone has had any experience with this.
>:> 
>:>			Allen Martin
>:>			amartin@wpi.wpi.edu
>:
>:No.  Consultron (CrossDos) syss that it will not work.  The AE drive will
>:read standart, 720k disks, just like an Amiga drive, but it won't read
>:the 1.44 meg IBM.  Consultron said it was because of the way they get 1.52
>:megs on a floppy was "signifigantly" different from the way big blue does
>:it. Hmmm.  I really wish I could use 1.44 megs disks.
>:
>Applied Engineering boobed when they desgined their high density drive.
>The way an IBM gets 1.44 megs onto a 3.5 inch disk is to slow it down to
>half the speed of a 720 K disk (rotational speed, not transfer speed).
>That way, they get 18 sectors per track instead of 9, and voila, twice the
>storage.

um, that's incorrect.  the way ibm systems get 1.44 megs on a 3.5" disk is
to double the data rate to the drive.  of course, the magnetic media has
to be able to handle it, and the drive's read/write electronics have to
be able to handle it.

>The Amiga puts 11 sectors per track on a 720K disk instead of 9, but it can
>read 9 sector per track formats.

the amiga puts one big "sector" on the disk - there are no sector marks
that the hardware searches for.  the amiga does not do partial track
reads or writes - it does only whole tracks.  elimination of the sector
marks and headers is where the amiga's disk format gains storage.

>To read 1.44 disks, you would need to slow our drives to half their speed,
>and then squeeze 22 Amiga sectors on each track, to enable you to read
>IBM 18 sector per track format.
>
>Applied Engineering got unreliable reads at that speed, so they didn't slow
>it quite that much, and only got 19 secotors per track.  Hence, 1.52 megs
>per disks.  However, also, it will not read the 1.44 disks because of the
>difference in speed.    
>
>Commodore's high density drive (standard equipment on the 3000UX) manages
>to get the reliable reads at that speed, and so can read 1.44 IBM disks,
>and also, as a bonus, you get the AmigaDos 1.76 megs/disk format.
>
>AE knew that CBM had to provide 1.44 disk compatibility to comply with
>UNIX SVR4 standards; they should have provided for it.
>
>
>--Chuck Cazabon, cazabon@hercules.cc.uregina.ca
>* My Opinions Are Not My Own...Feel Free To Plagiarize 

  --Scotty
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Scott Drysdale           Software Engineer
Commodore Amiga Inc.     UUCP {allegra|burdvax|rutgers|ihnp4}!cbmvax!drysdale
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