On 2 Oct 1998, Eric Smith wrote:
> Note that this doesn't deal with all of the weird Apple ][ copy protection
> schemes (like spiral tracks), but it will deal with some of them.
Theoretically you could simply scan half-tracks and quarter tracks and
just look for strong signals (something above a certain threshold).
> I have a twiggy disks for the Lisa 1 with a bad sector. I've always wondered
> whether hacking the drive electronics to allow software control over the
> read amplifier gain and/or data slice threshold would let me recover that
> sector.
I suppose it depends on what the problem is. I don't know how similar the
Twiggy encoding was to the Disk ][ encoding, but on the Apple ][, if I had
bad sectors on a disk, one way to attempt a repair would be to try to read
the sector over and over with the checksum disabled until the data looked
"right" and then writing it back to disk. This works a good percentage of
the time, but not always. Sometimes the disk is physically damaged, and
any bytes after the damaged portion of the sector get skewed and will
never translate correctly. I know there's some way to correct this but I
never sat down to analyze the problem and come up with a solution.
Sam Alternate e-mail: dastar_at_siconic.com
-------------------------------------------------------------------------------
Ever onward.
Coming in 1999: Vintage Computer Festival 3.0
See
http://www.vintage.org/vcf for details!
[Last web site update: 09/21/98]
Received on Thu Oct 01 1998 - 23:15:46 BST