8 Dec
2008
8 Dec
'08
3:45 p.m.
Philip Pemberton wrote:
Well, in a non-clean-room environment I've pulled the complete head stack out
of a drive and put it back in again with surprising success (said stack was
jammed solid with debris, so removing it to clean it all out was the only
way). Figured I had nothing to lose, and was surprised when the drive sprang
into life (and I got about 80-90% of the data back - and some of what I lost
was probably as a result of damage already sustained by the debris flying
around the innards of the drive)
The problem with PCI is licensing -- you need a PCI Vendor ID, which you
get by joining PCI-SIG, signing the patent licenses and so forth. The
damage? ?4k per year last time I checked.
Is that like Ethernet, though, where in theory you could just make up an ID if
in a closed environment, providing it didn't conflict with anything else - or
is there no 'hobbyist/prototype' ID set aside for this kind of thing?
(I suppose in a real Big Brother scenario, the people issuing the IDs would be
the same people as those who sold the ICs necessary to talk to the bus...)
No, but the service manual (with schematics) is on Bitsavers. I don't think
many of the other vendors ever took that approach, though (I don't recall
seeing any, actually, but I'm sure there must have been one or two).
Jules Richardson wrote:
Well presumably it doesn't vary *that* much, even on a flakey old drive...?
Yep. But I'm not sure that it's really
rocket science - assuming that
you know what encoding format the data's actually in, which is
probably the more difficult part. Coping with errors might be
interesting in some cases.
It isn't. The hardest part is converting from timing data back to an MFM
bitstream or binary data. You need to either handle changes in drive
speed in real time (i.e. track the read speed and continually adjust the
1t, 1.5t and 2t timing values) or do something similar to disk2fdi --
preprocess the data and figure out a set of thresholds that work,
assuming the disc is in good shape. Mmm, there's just a bit of a difference between
"what the math says" and
"what Murphy allows".
Heh, yeah...
The added board space is a bigger concern...
bah, stack one board atop the other with a bus between 'em ;)
I actually got banned from the school computer lab
many years ago for
allegedly destroying the hard drive in an Acorn A440. Said drive being a
20MB Kalok thing that was shaky at the best of times. I was dragged out
of class for half a day to help the "IT expert" (actually Just Another
Teacher [tm]) fix it. Most of that time was spent staring at !HForm's
soak-test screen and writing down all the errors, on IT Expert's orders.
One every two sectors IIRC.
"Make sure you don't get ANY of the numbers wrong! You have to re-enter
them when it actually formats the drive!"
I think in that situation I would have deliberately inverted the numbers
before handing the data over :-)
I'm not sure I ever had a Kalok drive, even in any of my Acorn stuff. My
loathing's reserved for the BASF units that Torch commonly used...
I'm not
sure how easy it is to tap into that kind of thing on a lot of
drives, though. Possibly best left for real emergencies on a
case-by-case basis...
It's "find a clean-room" territory. The head preamps are usually mounted
near the heads, often on the actuator arms themselves. Oh, food. A handful of pellets, a handful of fresh hay
and a fresh
bottle of water every 24 hours. Not hard, just expensive :)
I hear ya. Ours spend half their time outdoors, and at this time of year I
suppose they need to eat a lot. We've got a couple of dogs too - but then they
all make nice little portable space heaters :-)
That's probably worth looking into, but I know
very little about PCI
device design...
Ditto. Back in the day I wanted to get away from the internal card
approach - but these days it's possible to get a tiny, cheap
motherboard and should be relatively easy to build a networkable
"external device" that's a complete compact PC in its own right. Or you move to China, open a factory and pick a number
at random and
pray it doesn't clash with someone else's ID. Or pick one that isn't on
the Linux PCI Vendor ID list...
Grr, read entire message before typing reply, Jules... :-)
I'd say stuff it and make something up, assuming this is always going to be a
hobbyist thing rather than a serious commercial venture. Preferably make it
read from a ROM or other non-hard-coded system...
I think
I've got some Tandon and Epson drive schematics kicking around
and they used separate stages. But tapping into the head signal on a
floppy drive is a darn sight easier than a hard disk...
Mainly because the manuals for floppy drives tend to include
schematics... The ST412/506 OEM manual doesn't. Many a good idea has been born of idle speculation and
what-ifs.
... and of beer.