3 Jun
1998
3 Jun
'98
1:34 p.m.
MFM and RLL are encoding schemes. They define how to
turn a stream of 0's
and 1's into the magnetic patterns on the disk. They have nothing to do
with how a drive talks to its controller
Of course, I was just using the vernacular... (About like "CMOS setup" -
you didn't make any comments about that one though. :-)) But I didn't
remember that it was called ST506. Sounds like a Seagate part number.
Was it a PC hard drive, or even earlier?
When you low-level format a disk, you write the sector
headers and sector
data onto the disk. The sector headers typically contain information as
to which sector this is.
Hmmm, interesting. So low-level formatting doesn't rewrite these?
That would imply that the servo bursts are not involved in determining
sectors at all. I used to use an RLL card with a couple of formerly
MFM drives, and it made more sectors per track, so I thought the
wasted platter had something to do with that.
MFM drives usually use one side of one platter
just for these marks
Not normally. The sector headers are stuck in between the data blocks,
just like on a floppy disk.
You're probably thinking of the servo bursts - the signals that keep the
heads on a track. Some drives did use a particular side of one of the
platters for these. Other drives 'embedded' them in the sector headers on
the data platters. The latter is not common on ST506 interfaced drives,
but is common on SCSI/IDE drives
On a PC, if you need to low-level format an MFM drive there are several
options. Starting with the original XT controller, IBM set the standard
that BIOS code for doing that formatting would always start at a particular
address. So, you could use DOS's debug utility to simply execute the
Are you sure: While almost all clone controllers have a formatter routine
at C800:5, I couldn't find it in the original IBM XT hard
disk BIOS.
Hmmm. Well I think I remember using a full-length IBM controller with a
30 meg drive, and only being able to format 10 megs of it because it was
the XT controller designed for the 10 meg hard drive. But I don't remember
if I used debug to format it, or something else. This is my mom's machine
which she never uses, so one of these days I can replace it with something
more useful and refesh my memory about its contents. I'm going to try
to restore it to original condition since it is so close already.
Atari's are not my speciallity, but I seem to remember that the ST has a
'DMA port' which is somewhat SCSI-like. Most ST hard disk systems were a
SCSI host adapter followed by a SCSI -> ST506 (or whatever) interface
This guy's machine wasn't an ST I don't think, but that is what I have.
--
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