15 Jan
1999
15 Jan
'99
9:24 a.m.
When a drive seek fails, the drive first tries to read
the halftrack (recall
that Commodore disks are 48 tpi, not 96), then BUMPs out and back, tries to
read the sector, tries to read the half-track again, BUMPs out and back, and
so on, until it reaches a flag value stored in drive RAM, at which point it
declares the error. Very noisy, and the drive light flashes randomly during
this process.
Basicly the same on the Apple - just with a bigger problem: The
Disk ][ did 4 steps for every track, so quater tracks, and wrong
positioning by a quater of a track was possible. With some drives
the read signal was still readable a quater track aside, so you
could end up with a somewhat working disk where some tracks where
maladjusted - a horror when exchanging. Later on this was also used
as copy protection, to shift tracks - And there was also a programm
that modified DOS to write tracks closer (only 3 steps). Of course
completely incompatible, and _very_ drive and disk quality dependant.
Gruss
H.
--
Ich denke, also bin ich, also gut
HRK