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Re: Hardware musings
Michael J. Mahon wrote:
Ed Eastman wrote:
And this "evaluation" is a human or human-driven process, since it is
indeterminate when the program will actually do the verification.
(Sometimes it's well after boot time.)
Yes, this evaluation is done at the time the image is made. Right now
there is only a theoretical storage format to represent a protected disk
in it's entirety. By now _ALL_ apple II 5.25 floppy disk that have
protection have been produced and most of them have been hacked and
their general operation is understood even if not normalized and
deprotected fully. (Eg: I was never able to crack Silent service nor
normalize Prince of Persia.) But I can copy them.
No, since a file transfer is either good or not (much more likely to be
good), it is quite sufficient to simply checksum the whole thing.
True enough, but...
The only rational recovery in case of a bad transfer is to re-transfer
the file, which will almost certainly fix it unless it's bad at the
source.
That would be why. The checksum could tell you if the source itself is bad.
But you can tell a spiral disk from the sound... It is SOOO obvious.
And that is human observation, or one made *after* the image is created
by observing program behavior.
Before, I can lift the lid off my A2 drive and watch a normal and a
protected disk operate. (Don't try this with a CD!) I can even mark
the head position for different track locations. (I recall some
stickers one could buy for just such a thing.) Of course in today's
emulators you could certainly track the movements via software too.
No worries unless it is a spiral disk. Those images promise to be up
to 512k in size! (39x4 +1) x 6.25k
That's exactly what I'm thinking--and there's no foolproof way to
avoid saving that unless the image creator already (correctly)
understands the protection.
But ONLY the spiral images would contain that much information. Most
disk images will not.
But assuming the disk has ever been deprotected or even monitored
while booting, the protection routine will be known and where it is
at. Most protection schemes rely on data inserted between normal
sectors that does not get read by normal copy programs. The bit steam
format catches all of that.
Again, I think we'd all be better served by a format that didn't require
*any* knowledge of protection schemes (lest it be absent or incorrect).
Why? You would never need to save every possible bit location on a
diskette. The 1/4 tracking is almost irrelevant, each readable unique
track must be .75 tracks away form the next. Large gaps that would not
need be read. But of course this proposed format means we could.
For that matter if one were to read the whole thing, every .25 track
through trk 40, one could always purge unneeded tracks later. And in
the case of wide head tracks (where the signal is constant over several
tracks) you could simply copy track data form one to another to ensure
synchronization.
New formats anyone??
A person could even use this format to make distinctive tracks every
quarter track and have a HD floppy disk when done!
Thankx,
Ed