Path: utzoo!attcan!uunet!cbmvax!grr
From: grr@cbmvax.UUCP (George Robbins)
Newsgroups: comp.sys.amiga.tech
Subject: Re: A2090
Message-ID: <4763@cbmvax.UUCP>
Date: 17 Sep 88 02:48:09 GMT
References: <8809092138.AA05543@cory.Berkeley.EDU> <4702@cbmvax.UUCP> <9071@cup.portal.com>
Reply-To: grr@cbmvax.UUCP (George Robbins)
Organization: Commodore Technology, West Chester, PA
Lines: 31

In article <9071@cup.portal.com> thad@cup.portal.com writes:
> Sorry, the A2090 is *NOT* ST-412 compatible.
> 
> The major difference between ST-506 and ST-412 is that ST-506 supports only
> 8 heads (such as the older WD1010 controllers) and that ST-412 supports 16
> heads.

Sorry, wrong.  The main difference between the ST506 and ST412 is that
the ST412 supports buffered seeking, that is you can twiddle the step
line real fast and then wait of the drive to say it is ready instead of
having the count the milliseconds between step pulses.

The A2090 and almost any other controller you want to name do support
buffered seeks and are therefore ST412 compatible, so in a pracitical
sense, the difference between ST506 and ST412 is a historical
irrelevancy.

> The A2090 supports only 8 heads, thus is ST-506 compatible.
> 
> The Seagate ST-251 drive has 6 heads and will function with either an ST-506
> or ST-412 compatible controller.

That's more reasonable.  The 8+ head drives reassign one of the control
signals for the 3'rd head select line.  Traditionally, this has only
occurred on the high-capacity/high-doller drives by Maxtor and others,
but these drives are now showing up on the surplus market for ~$1K...

-- 
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)