Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!mordor!sri-spam!rutgers!husc6!m2c!ulowell!cbmvax!grr
From: grr@cbmvax.UUCP (George Robbins)
Newsgroups: comp.sys.amiga
Subject: Re: Amiga 2090 Controller Questions
Message-ID: <3240@cbmvax.UUCP>
Date: 31 Jan 88 04:39:15 GMT
References: <229@b11.UUCP>
Reply-To: grr@cbmvax.UUCP (George Robbins)
Organization: Commodore Technology, West Chester, PA
Lines: 33
Keywords: 2090 Controller

In article <229@b11.UUCP> jim@b11.UUCP (Jim Levie ) writes:
> I suppose that this is primarily directed at the CATS folks, but somebody
> else may also know the answers.
> 
> First of all where does the limit of 17 blocks (sectors) per track come from?
> Is it a hardware consideration in the ST506 circuitry or a software limit in
> the driver?  I tried an Atasi 3046 with the 2090, which works at 17 sectors
> per track, but not above.  The Atasi has over 10K bytes per track which should
> allow 20 sectors.

The 17 sector "limit" just reflects the number of sectors you get with
the standard ST506 clock rate, rotation speed and inter-block gaps.  To
go beyond these parameter requires some kind of special controller.  For
example "RLL" controller/drives change to data encoding format.  Adaptec
has sold controllers that vary the clock rate to put different numbers
of sectors on differend radial zones of the disk.

Typically the drives with "SCSI" interfaces use one of these or other
techniques to increase capacity, however the details are hidden between
the drive and SCSI controller, allowing the system to see a single
standardized interface.
 
> The 2090 manual is fine for installing and setting up the controller and
> drive, however there isn't any information about the Amiga Interface to the
> controller in the manual (csr's etc).  Any chance that this info is going to
> be released?

There's nothing secret about it.  I guess nobody's had the time or energy
to get all the random pieces together and write an intelligible document.

-- 
George Robbins - now working for,	uucp: {uunet|ihnp4|rutgers}!cbmvax!grr
but no way officially representing	arpa: cbmvax!grr@uunet.uu.net
Commodore, Engineering Department	fone: 215-431-9255 (only by moonlite)