Path: utzoo!mnetor!uunet!husc6!bloom-beacon!oberon!pollux.usc.edu!papa
From: papa@pollux.usc.edu (Marco Papa)
Newsgroups: comp.sys.amiga
Subject: Re: Now what?  (Hard Disk woes.)
Message-ID: <7434@oberon.USC.EDU>
Date: 5 Mar 88 20:53:06 GMT
References: <oWA4lWy00V4E89s0OA@andrew.cmu.edu>
Sender: news@oberon.USC.EDU
Reply-To: papa@pollux.usc.edu (Marco Papa)
Organization: Felsina Software, Los Angeles, CA
Lines: 58

In article <oWA4lWy00V4E89s0OA@andrew.cmu.edu> dg2l+@andrew.cmu.edu (Douglas Phillip Ghormley) writes:
>
>In article <4269@dandelion.CI.COM>, dgg@dandelion.CI.COM (Dave Grubbs) writes:
>>Problem #1:	It is only 30Meg when using RLL and the 2090 controller can
>>		only deal with MFM format.  So I have a fast 20Meg hard disk.
>>		Is there anything I have to do to set "MFM"?  Nothing is
>>		very clear in their manual.
>
>Pardon my invincible naivity, but what is RLL and MFM and how do you tell 
>which type a given hard drive is?  I thought all hard disks would work with 
>the A2090.  No?

MFM and RLL (Run Length Limited) generally refer to both the controller and
the drive.  Quoting the Seagate Installation Handbook:

"To achieve full performance with an MFM drive you must use an MFM controller
which operates the ST412/MFM interface at 5.0 megabitssec.  ... Operation of
an MFM drive with an RLL controller is not approved by Seagate and may void 
your warranty".

"To achieve full performance with ann RLL drive you must use and RLL controller
whichj operates the ST412/RLL interface at 7.5 megabits/sec. Only drives
with an R appended to the product nuber are designed and certified for use 
with an RLL controller. ... Operation of an RLL drive at data rates other 
than 7.5 megabits/sec. or operation of an RLL drive with an MFM controller 
is not approved by Seagate and may void your warranty."

The Commodore A2090 Hard Disk controller is ST506/ST412/MFM and SCSI (ANSI
X3T9.2) compatible.  It is not ST412/RLL compatible.  In general taking
two drives with the same UNFORMATTED capacity, one RLL and one MFM, the RLL
drive will have a larger FORMATTED capacity.  Also, in general, using an
RLL drive with an MFM controller might work, IF AND ONLY IF the drive has
had an MFM LOW-LEVEL FORMATTING.  Using an RLL drive that has been LOW-LEVEL
FORMATTED with RLL won't work with an MFM drive.  As you see from above,
Seagate does NOT "approve" this and doing it will void your Seagate warranty.

The viceversa, using an MFM drive with an RLL controller, will NEVER work.

Seagate drives, for example, come low-level preformatted at the factory, with
an included bad block table.  The ST251, and 40 M MFM drive, comes MFM 
low-level preformatted. The ST238R, and 31M RLL drive, comes RLL low-level
preformatted.

Moreover, for optimum performance, ST412/MFM drives REQUIRE write 
precompensation, while RLL and SCSI drives don't.

> (While we're at it, is there an upper limit to what the 2090 
>can control?  i.e. 60Megs)  Any other peculiarities?

The current hddisk.device driver supplied with the A2090 controller has a
built-in limit of about 54 Meg (or something close to that) PER PARTITION.
Therefore, if you have a large capacity drive, let's say 120 Meg, PREP'it
with multiple partitions.  This is also a good idea in general, since it
will cut down the seek time, if a file is scattered throughout the drive.

I hope this clears the question a bit.

-- Marco