Thread by @a2_4am

So here's a flux image of a typical protected disk by Sunburst Communications. Several things of note:

1. It is fundamentally a 16-sector disk. You can see the 16 sections of each ring (track), like an unprotected disk.

However...

2. On a regular disk, and even most copy protected disks, each sector is delimited by a stream of $FF nibbles. At a very low level, these are used to synchronize the disk reading routines after moving to a different track. On Sunburst disks, those delimiters are blank...

...not empty, but actually blank — a relatively long series of 0 bits, except the Apple II disk drive can't handle any more than two 0 bits in a row, so when it reads them back it randomly starts inserting 1 bits. Disks that returned random data confused copy programs to no end.

Halfway through the disk (track 0x11, out of 0x22), there's a longer black mark, even longer empty space. Sunburst disks had no sector $0F on track $11, which — even if you managed to copy the disk — would confuse third-party programs that assumed the disk directory was there.

4. More difficult to see, but if you know what to look for, you'll see that all the tracks after 0x11 (towards the center of the image) are shifted, because the data on those tracks was stored on the "half-track" above where it belonged. Track 0x12 data was on 0x12½, and so on.

All of this added up to disks that were incredibly difficult to copy with third-party programs back in the day. Since the programs themselves were generally educational (and not the fun kind), pirates skipped them. 35+ years later, few Sunburst disks were digitally preserved.

I have only ever seen a handful of homemade "protected backups" of Sunburst disks. They're incredibly rare. On the other hand, I've seen hundreds of disks from DLM, Hartley, Peachtree, and other top eduware vendors. But not Sunburst. Sunburst stands alone. Copy protection works.

In the past 12 months, we've moved to preserving Apple II disks digitally, with copy protection intact (via Applesauce flux imager by @DiskBlitz). But we still can't create bootable .woz files from these flux images, because the protection is so ridiculous. Hopefully soon.

/fin