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Path: utzoo!watmath!clyde!cbatt!ihnp4!inuxc!inuxh!rdr
From: rdr@inuxh.UUCP
Newsgroups: comp.sys.misc
Subject: Re: ST412 vs. ST506 interface
Message-ID: <515@inuxh.UUCP>
Date: Wed, 10-Dec-86 13:12:48 EST
Article-I.D.: inuxh.515
Posted: Wed Dec 10 13:12:48 1986
Date-Received: Sun, 14-Dec-86 07:35:42 EST
References: <7200001@fthood>
Organization: AT&T Consumer Products, Indianapolis
Lines: 29

> 
> HELP!   I just purchased a hard disk with an 'ST412' interface.  It seems
> that my controller will accept only a 'ST506' drive.   What is the 
> difference in the interfaces?  Is there modifications possible, or am I
> doomed to return the drive?
> 
> The drive is a Seagate ST251, the computer is an AT&T Unix PC 7300 (with
> the controller built into the mother board.
> 
There should be no problem there - I've done it before, though the specific
drive and controller were different.  What you can't do is put an ST506
drive on an ST412 controller.  The difference between 506 and 412 is small -
the 412 supports a "buffered seek" capability.  This allows a controller to
tell a drive to step the head many tracks at a time by sending all the
step pulses very quickly - much faster than the drive can actually step.
The 412 drive has enough smarts to buffer all the steps and move the head
in one operation, rather than stopping at all the intermediate tracks.  The
reason you shouldn't have a problem is than your 506 controller simply won't
send step pulses faster than the drive can step a track-at-a-time.  The
worst that happens is your controller won't move the head as fast as the
drive could handle.

Have you actually tried it?  If so and it didn't work, then it's hard to
say what your problem is, but I doubt it's the 506/412 mismatch.  BTW,
my experience was with a CMI 30meg drive for an AT, on a DTC5150BX
controller in an AT&T 6300.  Worked fine.

Bob Rindfuss
...ihnp4!inuxh!rdr