Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!mit-eddie!bloom-beacon!apple!amdahl!kevin
From: kevin@uts.amdahl.com (Kevin Clague)
Newsgroups: comp.sys.amiga
Subject: Re: 15 Head Hard drive and the A2090(a)
Message-ID: <040b02ba29ZN01@amdahl.uts.amdahl.com>
Date: 19 May 89 14:38:42 GMT
References: <1735@dciem.dciem.dnd.ca> <680@dialog.UUCP>
Reply-To: kevin@amdahl.uts.amdahl.com (Kevin Clague)
Organization: Amdahl Corporation,  Sunnyvale, CA 94086
Lines: 53

In article <680@dialog.UUCP> root@dialog.UUCP (Christian Motz) writes:
>In article <1735@dciem.dciem.dnd.ca> kevin@dciem.dciem.dnd.ca (Wallace B. Wallace) writes:
>>I recently acquired a 15 head Hard Drive for my Amiga 2000 only to discover
>>that the A2090(a) does not support >8 heads.  Has anyone figured out either
>>(1) a way around this or (2) a different product that does support it?
>>Any updates on an upgrade of the A2090(a) that will support them?  I'd hate
>>to lose half of my storage even if I can upgrade it later.
>>   BTW, the drive is a Fujitsu 2249SA, SCSI, 320M, 8 disks, 15 heads
>
>The standard ST506 does support only 8 heads by definition. Since the A2090
>has a "true" ST506 interface onboard, it complies with this standard. I do
>not think that C=A will ever "fix" this (there really is no needt to change
>this). But since your drive is an SCSI-drive anyway, this limitation does
>not apply. The 2090 can handle SCSI-Drives of almost any size. So, go ahead,
>hook it up and you'll see that you get your full 320 MByte of capacity.
>
>--
>Christian Motz       uucp: ...!uunet!mcvax!unido!pfm!nadia!dialog!root
>"Trust me, I know what I'm doing!" -- Sledge Hammer         Bix: cmotz

I have a 2090A controller, and once I got it installed and configured,
EVERTHING was great, BUT it was not a simple install.

The 2090A's biggest problem is it's poor documentation.  Nowhere in
the dos do they tell you that the only specs that matter with a
SCSI device is block size and number of blocks.  You can factor out
the number of blocks on the device into
the number of heads, number of blocks per track and number of
cylinders any way you want.

I went so far as to try 1 head, 1 block per track, and some
huge number of cylinders for my Quantum 80S drive.  It worked fine.
Seems kinda silly though.

For simplicity, the 2090A and hddisk.device use this heads, blocks,
cylinders format so that at some level, the st506 and SCSI drives
look the same.  Somewhere in the process, the controler/device driver
convert this into block number and use that when talking to SCSI
devices.

The moral is that you can lie all you want about the physical
configuration of a SCSI drive.  The only NO-NO is to tell the
system that the drive has more blocks than it has.

Kevin
-- 
UUCP:  kevin@uts.amdahl.com
  or:  {sun,decwrl,hplabs,pyramid,seismo,oliveb}!amdahl!kevin
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[  Any thoughts or opinions which may or may not have been expressed  ]
[  herein are my own.  They are not necessarily those of my employer. ]