KryoFlux - Commodore 64 - Mastered Tracks

2009-11-15

We’ve been testing the recent new features on some Commodore 64 disks.

It’s very interesting to see how tracks were commercially mastered by looking at the flux reversal counts. Each written track on the same side will have a similar number, and you can see how half-tracks are unwritten.

The correct tracks are:

00.0: track 1 
01.0: noise/left over content 
02.0: track 2 
03.0: noise/left over content 
04.0: track 3 
05.0: noise/left over content 
...

You can also see another phenomenon. Tracks written on 40-track drives will have almost identical content for half-tracks. We have experience recovering data on the Commodore 1541 by reading half-tracks, as sometimes it was still readable when the original was not...! Now you can see that this is really true.

00.0: track 1 
01.0: track 1 misaligned 
02.0: track 2 
03.0: track 2 misaligned 
04.0: track 3 
05.0: track 3 misaligned 
...

The zoning is very visible too.

While we were at it, we made the index signal sampling even more accurate. After these changes 3.5” drives show drift values of nanoseconds (that is just a statistical artefact, it’s not really that low). On the other hand 5.25” drives give about 5us drift on average. We are fairly sure this is down to having incorrect signal levels generating changes way too quickly.