Re: Toy Shop

[Toinet <antoine.vignau@laposte.net>]

"Vlad, are you there? Can you tell us what you do to preserve your
original 5"25 disks?"
"Vlad, are you there? Can you tell us what you do to preserve your
original 5"25 disks?"
"Vlad, are you there? Can you tell us what you do to preserve your
original 5"25 disks?"

The subject: how to get the most of our disks and ensure writing it
back to disk?

Reading a track is easy, but as already written by others, getting the
"real" stored data is another story due to the way the protection was
done.

If the protection deals with normal nibbles (therefore normal bits),
we will have no trouble in getting an exact copy of a disk. On the
contrary, if the protection goes beyond what the LSS normally offers
(therefore playing at the bit level, e.g. desync) then it is more
difficult to get the exact data, multiple reads may help but that
would generate big files.

As far as full track vs half-track vs quarter-track is concerned, I
believe that a step of a half-track is sufficient to get data. The
head size of the drive is large and will read the data where the head
is placed but also the adjacent data.

And for track sync, track start address or track length, I believe
that it is a false problem. With a standard RPM of 150 for the drive,
with 4us per bit, you can write a little bit more than 18 sectors (6*2
coded or 342 nibbles) for a total of, let's round it to the huge 6500
nibbles per track. Now, let's compare it with the number of nibbles
EDD reads per track: 14336 (from $4000 to $77FF in memory) That is
more than 2 times what a track can hold, that also means we should
have all the nibbles of a track and probably handles the major part of
on-disk protection schemes.