The .woz Format – Accurate Preservation of Apple II Floppy Disks #Apple #VintageComputing #RetroComputing

Images via https://twitter.com/a2_4am/status/1485090945179607042

Nerdly Pleasures discusses the .woz data format, which is an accurate way to preserve Apple II floppy disks.

Floppy disks were not designed to store data for forty plus years, but for the oldest home computer systems like the Apple II, most of its software is at least thirty years old.  But it is not preservation merely to dump a copy of a game which was pirated in the day.  Those games usually have “cracktros” which do not represent the developer’s intended presentation of the game, may have cut out elements of the original game to save space or may include corrupt data in them.  Ideally one should have a proper image of original disks with all data preserved.  Of course, from almost the earliest days of the Apple II’s Disk II drive, copy protection schemes were implemented on commercial software to prevent casual disk copying.  True preservation requires preserving them as well, and that requires emulation to become more accurate than it needed to be for just sector based .dsk images.

Wozniak used the floppy drive in ways unique to that system and dissimilar to other computers.

Almost every disk drive ever made has at least two motors, one to spin the disk, the other to position the read/write head.  The Apple II’s Disk II drive is no exception to this general principle, but the manner in which it controls the read/write head motor is very unusual for a consumer-based drive.  Most home computers issue a command to the drive interface for the head to change to the next track, the previous track or back to track #0.  Their disk drives and controllers have sufficient capabilities to be able to position the head over the surface of a disk so that track 1 did not overlap track 2 and so on.

But the Apple II’s disk drive came from an earlier time when drive electronics were not so sophisticated.  Steve Wozniak based the Disk II on the earliest 5.25″ floppy drive, the Shugart Associates SA400, taking the drive mechanics but ditching the sophisticated controller board and using his own simpler and cheaper board.

Many copy protected games use synchronization tricks that could only work reliably on disks duplicated on professional-grade equipment.

Read all the details in the thorough guide on Nerdly Pleasures.


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