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Re: Hardware musings
Matthew Russotto wrote:
In article <tKOdnRHlve84vKrYnZ2dnUVZ_rOdnZ2d@comcast.com>,
Michael J. Mahon <mjmahon@aol.com> wrote:
Unfortunately, I don't think it's an easy problem to take image
data for all quarter tracks, together with sync info and soft bit
info, and turn it back into a physical disk that, when imaged,
would create the same file that produced it.
A relatively simple problem is that to control automatically even
the approximate track length in bits requires writing with a variable
clock (quite doable with a microcontroller).
I think it's the figuring out what's on there in the first
place which is the problem. You'd probably need to read each quarter track,
and sample (at much higher frequency than the Disk II data rate) the
_analog_ value of the data from the drive head (not just the field
transitions but the field strength). This would tell you with high
confidence which quarter-tracks actually held data, and give you
track length data and even "holes" where data wasn't written. Anyone
up to building such a thing?
No, it's only necessary to sample the disk with a Disk ][ Controller,
since that's the only instrument that the copy-protected program has
to observe the disk.
If you sample *everything* that could possibly be read, then you are
ready to accurately simulate what the program would have observed if
it had read a physical disk, doing whatever it does.
Part of the problem is that data read from a "track overlap" region
will be an artifact of the micro-variations in rotation speed of the
drive on which it was written, and there is no way to control that
on the writing drive (floppy drives don't have a way to read adjacent
data as new data is being written).
Fortunately, you only have to be able to duplicate what disk
duplicators of the day were capable of duplicating reliably.
Not necessarily so--unless you know that there were no disks
written directly by Apple II's.
And if you *do* know that, then you still have to know all the
capabilites of all the disk duplication machines...somehow,
large quantities of "spiral tracked" disks were produced. ;-)
-michael
NadaNet networking for Apple II computers!
Home page: http://members.aol.com/MJMahon/
"The wastebasket is our most important design
tool--and it's seriously underused."