RLL vs. MFM

[Ethan Dicks]

On Tue, 8 Mar 2005 22:57:20 +0000 (GMT), Tony Duell
<ard at p850ug1.demon.co.uk> wrote:
> >
> > No you can't use a RLL with an MFM controller. Similar but not the same.
> 
> Sure you can.
> 
> If the interface is the same (most likely the ST506/ST412 interface
> here), then you can use an RLL-capable drive with an MFM controller. You
> won't be able to read what's on the drive, you'll have to low-level
> format it, and you'll only get about 2/3s the stated capacity. But if
> you're trying to replace a hard drive in some old machine with an MFM
> controller and you happen to have an RLL-capable drive around, it'll work.

Some people even did it on purpose, back in the day... I remember
people putting a
Seagate ST-238R on an MFM controller and getting the expected 21.4MB.  The
reason for doing it on purpose was to de-rate the drive in the
expectation of fewer
bad blocks, and longer-term reliability.  Dunno if that really works,
but at the time,
there was this expectation that it should work, certainly better than
trying to format
an ST-225 as if it were an ST-238R. (I think it was assumed that Seagate already
had qualified their own platters and labelled the drives accordingly)

-ethan