29 Oct
2008
29 Oct
'08
5:22 p.m.
On 29 Oct 2008 at 23:23, ethan.dicks at usap.gov wrote:
I don't know anything about the HP9133D, but I did
fiddle with
plenty of MFM and RLL drives on ISA controllers and non-PC
controllers (DEC RQDXn, Commodore D9060/D9090, Dialog DQ614, etc.,
etc.) There was no hard and fast rule that X drive could always
be replaced by Y drive of a larger size, but there were many
specific cases where it worked - one I've done is replacing a
Tandon TM602S with a Seagate ST225 in a Commodore D9060. They
have the same number of heads (4), and although the ST225 is 20MB
and the TM602S is 5MB, what you end up with is a 75%-unused
ST225, and there's no conflict between the Write Precomp and the
RWC parameters.
In general, it's useful to think of MFM drives as being large, fast
floppies in that by and large, they consist of two parts--the drive-
selection, head positioning and side-select electronics and the
read/write electronics. The drive is pretty much blind to the data
being placed on it, like a floppy. So picking a drive that meets or
exceeds the original in all of the parameters generally works pretty
well. Unlike ESDI, IDE and SCSI drives, there is no "identify"
facility in an MFM drive. If you want to figure out the capacity the
hard way, you can try seeking to successively higher cylinders and
tracks until you hit an error (a binary search will speed the process
up).
There are some exceptions--one of which is the MFM drives used on the
"baby" models of the DG MV series. Apparently (as nearly as I can
determine), the controller firmware looks for a specially formatted
track that contains the drive parameters--just plonking an off-the-
shelf drive of the same model number just doesn't work. The other
exception that comes to mind are drives that have a higher rotation
speed than the customary 3600 RPM.
Whether or not the HP drive in question falls in this latter
category, I am unable to say.
Cheers,
Chuck