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A commercial-based floppy duplicator is not so limited, it can be programmed to synchronize tracks and sectors in a predictable manner. When a consumer based floppy drive without an index hole sensor writes track, each sector 0 on track will almost certainly be offset from the previous track by some random amount. Steve Wozniak removed the index sector hole sensor to save cost on the Disk II drive, but neither Atari nor Commodore 8-bit computers have an index sector hole sensor either.

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While convenient, this was not strictly necessary as software could determine the location of sector 0 by reading sector index data stored on a disk in between sector data areas. Computers that could use the index hole would write sector 0 aligned to that hole. Essentially when the hole emitted light from an LED to a phototransceiver, that would tell the computer that the disk is at a physically known location. The sector index hole was a hole punched through the jacket and the surface of the floppy disk which could be viewed by an optical sensor in the drive. In addition, many floppy drives came with a sector index hole. The Commodore 1541 was also notorious for using this method to find track 0. The characteristic stutter when a Disk II drive is powered on is due to the drive head being knocked against the forward end of the rails several times to ensure the head is positioned over track 0 on the outer edge of the disk.

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The Disk II, unlike an IBM PC drive, cannot tell the system that it has reached track 0, so when power is applied to the Drive, it is sent more than enough phase changes to ensure it reaches track 0. Of course, if a programmer did not want to interact with the disk drive at such a low level, the Disk Operating System's (DOS) Read-Write-Track-Sector (RWTS) routines provided a higher level abstraction to disk drive operations. The SA400 and its later IBM-derived drives like the Tandon TM100-2 just have one signal line for stepping and one line for the direction and let the drive's controller handle the phases.

The Apple II's Disk II Controller card provided softswitches to manipulate the phases. To move a standard 5.25' track width, one had to toggle all four phases in software in a particular order and with careful timing.

The Disk II uses a four-phase stepper motor, and toggling a phase turns the motor a one-quarter turn in one direction or the other. 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. 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.īut the Apple II's disk drive came from an earlier time when drive electronics were not so sophisticated. 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. 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. woz images are made.Īlmost every disk drive ever made has at least two motors, one to spin the disk, the other to position the read/write head. In this blog article I will describe in as much detail as I can how the Disk II Floppy Drive works, how it is different from floppy drives for other systems, how data is stored on disk, the benefits of the. True preservation requires preserving them as well, and that requires emulation to become more accurate than it needed to be for just sector based.

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. Ideally one should have a proper image of original disks with all data preserved.

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. But it is not preservation merely to dump a copy of a game which was pirated in the day.

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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.

The need for proper preservation of floppy-based software cannot be understated.