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From: easton@zds-oem.zds.com (Jeff Easton)
Newsgroups: comp.sys.amiga.emulations
Subject: Re: Question about Cross-Dos
Message-ID: <1991Jun12.123802.14255@zds-oem.zds.com>
Date: 12 Jun 91 12:38:02 GMT
References: <1991Jun11.215637.563@wpi.WPI.EDU> <1991Jun12.001931.3711@ucselx.sdsu.edu> <507@regina.uregina.ca>
Organization: Zenith Data Systems, OEM Systems Engineering
Lines: 57

In article <507@regina.uregina.ca> cazabon@hercules.uregina.ca (Charles Cazabon (186-003-526)) writes:

>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.

  Er,  The IBM style 1.44 Mb disks have the same rotational speed as 
720K drives.  The data transfer rate was doubled to obtain HD.  The same
is true of the new 2.88 Mb drives as well.  The transfer rate was doubled 
again.

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

  Correct.  See below.

>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.    

  If I recall the previous discussions correctly, the Amiga cannot 
directly connect a IBM 1.44 Mb drive (and use the 1.44Mb storage) because
the custom chips are fixed at a data transfer rate of 250 kbits/sec.  HD
transfers at 500 kbits/sec (thus the halving of rotational speed for
the Amiga drive) and ED is 1 Mbit/sec.

  The downside to all this is that the Commodore version of a 1.44 Mb 
drive will read/write the HD disk twice as slow as a true IBM can.  This
assumes that everything but the transfer rate is the same, which I'm
sure isnt the case :-).

>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.

  Is this shipping now in the UX?  If so, where can I get one for my
regular old A3000?  Is there any Amiga DOS drivers needed to support it?

>--Chuck Cazabon, cazabon@hercules.cc.uregina.ca


        Jeff Easton               Zenith Data Systems
     // Systems Engineer 
   \X/  easton%zds-oem@caspian.cs.andrews.edu
	easton@andrews.edu	
   What?  Preemptive Multitasking in only 256K of RAM?  :^)  :^)

  Disclaimer:  I dont work in Drive Evaluation. :-)