HI, Guys,
MFM and RLL are, indeed, very similar, but not exactly compatible.
Theoretically, you should be able to get any MFM drive to work on any MFM
controller as long as that controller can support the formatting parameters
required by the drive. However, you have to start from scratch, with that
low-level format, which could be done via a software package, or by the
debug routine already described earlier.
In the case of the Seagate drives, the ST-225 is the MFM model, with the 25
part desciring the unformatted capacity of the drive. You would get
anywhere from 2,300,00 or so bytes to 21,400,000 bytes formatted capacity
depending on how the controller used recognized and formatted the drive.
Once formatted on a given controller, the drive would work only on that
controller. It would be a gamble equivallent to buying a lottery ticket and
winning the 160-million dollar jackpot if per chance you connected that
drive to a different MFM controller and it worked without reformatting.
The RLL version of the ST-225 was the Seagate ST-238, with the unformatted
capacity being 38MB. Physically, the drives are the same in every respect,
except that the magnetic coating on the ST-238 is of a higher quality and a
finer consistency so that more data can be squeezed into a smaller space
without overwriting, crosstalk, and other error-causing problems. Believe
me, if you want to put an MFM drive on an RLL controller and format it to
the higher density, don't do it with any material you don't have completely
backed up somewhere else, or anything that must remain reliably intact. As
IBM used to be fond of saying when you used something not officially
supported, "Results may be unpredictable!"
I don't remember exactly the differences between an MFM and an RLL
controller, except that there would be different BIOS chips on it, and
usually, the more expensive RLL controller would be prominently labelled as
such.
The Seagate ST-225 made its debut in late 1985 or maybe in 1986. It took
the PC world by storm because for around $400 or so, you got a 20MB drive in
a half-height form factor which was cheaper than most companies' hulking
full-height 10MB drives. Wow! Not only could you get a 20MB drive cheap!,
you could put two of them in the space occupied by one of anybody else's
drives! Remember, those were the days of the $2,000-dollar XT, the 360KB
floppy drive, and a time when you could run DOS, Lotus 1,2,3, DBase II, a
word processor, a few games, a little comm program, on a 5MB drive, and
still have lots of disk space free for your data. I remember the wonderment
in people's voices when they would exclaim about how they couldn't imagine
how they'd ever fill up that monster-capacity disk!
That ST-225 does not have self-parking heads, so you'll want to chase down
that park.com or parkhead.exe or park.exe utility to do it for you when you
shut down. The heads are moved by a stepper motor, and over time, they tend
to drift, so they reccommended a high-level format of the drive at least
once a year or so, after backing up your stuff first--of course! I have a
Dell system 200 12.5MHz 80286 machine that has a still-working Seagate
ST-225, so they were definitely made of solid stuff and justly famous for
their reliability. Of course, they made millions of them, andprobably did
not stop making them until somewhere between 1989 and 1991, so you'll still
find them. Nine out of ten XT and 286 desktop machines I've seen have had a
Seagate ST-225 inside, sometimes two of them. Another advantage they had
was that they consistently shipped with fewer bad sectors from the factory
than most other drives at the time for under about $800.
Have fun playing with that old Dino!
Reply to: [EMAIL PROTECTED]
Brent Reynolds, Atlanta, GA USA
Jurasic Pork--- It's been in the fridge a LONG time.
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