--- Eric Smith <eric_at_brouhaha.com> wrote:
> Gordon Zaft <zaft_at_azstarnet.com> wrote:
> > As far as I know, the RD54 (aka Maxtor something or other, or
> > Priam 519, or other similar) was the largest MFM drive ever made.
>
> Not even close. For example, the Fujitsu Eagle (M2351) had a capacity
> of 380 MB, vs. 150 MB for the Maxtor XT-2190.
There was a Fuji MFM drive also called the Eagle? When I think of
an "Eagle", I think of the ~10" platter, 10.5" tall, 19" wide SMD
drive that clocks in around 400MB - I have several of them, and
some SI9900 controllers with Massbus cards.
> I'm pretty sure there were other drives using MFM had even higher
> capacity.
I wouldn't claim that the XT2190 was the absolute largest capacity
MFM drive, but it's pretty close, ISTR. Right about the time that
16 heads by 1024 cyls was about the largest you could get is when
ESDI began to take over the large end of the small computer market
and IDE began to take over the small end.
> Of course, modern drives use RLL rather than MFM because they can get
> 50-100% better data density... And they use ZBR to pack more data into
> the outer cyclinders, whereas MFM drives generally used the same data
> rate on all cylinders.
Modern drives do indeed use all those tricks (and some older drives, too;
the Commodore 1541 has 4 bit densities to pack a variable number of
sectors per track depending on the physical track length at a given
radius). The important thing is to not violate the linear bit density
of the media. Once you have that figured out, you can add another sector
every few tracks.
I am fairly certain that all MFM drives use a clocked data rate that
ensures the bits on the inner tracks aren't too close together for
the capabilities of the media and heads to discriminate. It's easier
to build a disk controller when you don't have to calculate on the fly
where your sector might be, but it's a poor use of the disk from a
magnetic domain standpoint.
-ethan
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Received on Fri Jul 12 2002 - 15:15:56 BST