19 Jun
2010
19 Jun
'10
12:59 p.m.
On 19 Jun 2010 at 11:53, Fred Cisin wrote:
...tell you that "the
computer is a Lear-Sigler with a Northstar Horizon external drive"...
Just getting them to NAME the computer is a struggle.
I gave up on a customer who insisted strenuously that his system was
a "Hazeltine 1400". He absolutely refused to look for another name.
Chuck is very fond of histograms.
If it doesn't pass the MFM test, that's the first place I go. 2
peaks=probably FM, 3 peaks = probably MFM, 4 peaks = probably MMFM.
5 peaks = maybe GCR.
But I'm not often interested in *writing* floppies, though I can do
it if you cross my palm with silver. (e.g. Customer wants copies of
his hard-sector 8" disks). What I'm mostly interested in is getting
the data off of the disk, which can extend past simply figuring out
the filesystem and transferring the files. Right now, I'm dealing
with some sort of tokenized test language. Fortunately, the customer
still has printouts of some of his files, so I can figure a fair
amount out.
On the other hand, I hardly ever continued with any
format that wasn't
going to be possible to convert using relatively stock hardware. "If
it isn't IBM/WD, then just file the disk in the appropriate section of
hardware incompatibles."
On occasion, I have to build something to handle a peculiar setup.
Catweasels aren't the end-all, nor are any others. For example, try
putting a Catweasel on a 2.8" DataDisk drive.
I'm surprised that no one's showed up with some floppies from a
Memorex 651 drive yet.
I played around with some probabalistic code to come
up with what to
try first, particularly in finding and identifying software sector
interleaves (which sector is used after sector number 1? Feed the
code the start and end bytes of sectors and have it identify which
ones are most likely to be "half a worm" (start of a "word" at the
end
of one sector, end of the word at the beginning of another sector); in
the absence of adequate langauage text (or excessively unfamiliar
languages) multibyte machine language instructions are adequate)
The fun ones are where there's a sector interleave and a side and
cylinder skew. Or where tracks are allocated on alternate sides of a
directory that's located in the middle of the disk.
But for file information, nothing beats the human
mind.
It's great fun if you're the sort of person who can look at a problem
and have the patience to wait for an "ah hah!" moment rather than
trying to beat it to death. If you're the "gotta solve it now" type
of person, you're probably in for a lot of headaches.
Cheers,
Chuck