Apple FileWare

FileWare floppy disk drives and diskettes were designed by Apple Computer as a higher performance alternative to the Disk II and Disk III floppy systems used on the Apple II and Apple III microcomputers. The drives were also referred to as Apple 871 drives in service documentation [Apple Computer Inc.: Lisa schematics, 1981] , based on their approximate formatted storage capacity in kilobytes, but were most commonly known by their code name, "Twiggy".

History

In 1978, Apple intended to develop its own FileWare drive mechanism for use in the new Apple /// and Lisa business computers being developed. They quickly ran into difficulties which precluded them from being incorporated in the Apple ///, which continued to use the earlier Shugart design. [ [http://home.socal.rr.com/fuweb/floppysite/twiggy.html Apple and the Floppy Drive ] ] FileWare drives were finally introduced with the Apple Lisa computer in 1983, and were used in prototypes of the Apple Macintosh. Although Apple planned to make FileWare drives available for the Apple II and Apple III, and announced them under the names UniFile and DuoFile (for single and dual drives, respectively), these products were never shipped. [ [http://www.apple2world.jp/apple2/COL/MapItems/lisa2/lisa2.html Lisa2 ] ]

Drive

FileWare drives are 5¼ inch double-sided, but are not mechanically compatible with industry-standard diskettes. In a single-sided floppy disk drive, the disk head is opposed by a foam pressure pad. In a normal double-sided floppy disk drive, the top and bottom heads are almost directly opposed to each other. Apple was concerned about head wear, and instead designed the FileWare drive such that the top and bottom heads are on opposite sides of the spindle, and each is opposed by a pressure pad. Since there is only one actuator to move the heads, when one head is near the spindle, the other is near the outer rim of the disk. [Apple Computer Inc.: Lisa Hardware Reference Manual, 1983]

The drive is approximately the same size as a standard full-height 5¼ inch floppy drive, but does not use the standard mounting hole locations. The electrical interface is completely different than that of standard drives, though conceptually similar to that of the Disk II.

Diskette

The FileWare diskette has the same overall jacket dimensions of a normal 5¼ inch diskette, but because of the head arrangement, the jacket has non-standard cutouts for the heads, with two sets of cutouts on opposite sides of the spindle hole. The write enable sensor is also in a non-standard location, though most FileWare diskettes were produced without a write protect slot. The jacket had a corner cutout that keyed the diskette to prevent insertion in an incorrect orientation, and a rectangular hole that the drive could use to latch the diskette in place, preventing removal until the software allowed it.

FileWare drives used 62.5 tracks per inch rather than the standard 48 or 96 TPI, and used high flux density (comparable to the later IBM 1.2MB format introduced with the PC/AT). This required custom high-density media. The coercivity required is similar to that of the 1.2MB format, so it is possible to modify the jacket of 1.2MB diskettes for use in a FileWare drive.

Format

The disk format used GCR in a manner very similar to that of the Disk II. The drive contained circuitry to allow software control over the motor speed, which was used to maintain near constant flux transition rate on all tracks, so that more data could be stored on the outer tracks.

Each physical sector stored 512 data bytes and 20 tag bytes. The controller used similar circuitry to the Disk II controller, but ran at twice the clock rate. The controller used a dedicated 6504 microprocessor; in the Lisa this was on the system I/O card, and for the UniFile/DuoFile products, it was on an interface card that plugged into a peripheral expansion slot. The Lisa 2/10 and Macintosh XL I/O card used the IWM controller chip to replace the TTL chips of the earlier design.

Reliability

In the field, the FileWare drives proved to be somewhat unreliable. In early 1984, Apple introduced the Lisa 2, which used a single 3.5 inch Sony floppy drive in place of the two FileWare drives of the original Lisa. A free upgrade was offered to Lisa 1 owners. The Macintosh was also introduced using the Sony floppy drive. [ [http://www.brouhaha.com/~eric/retrocomputing/lisa/twiggy.html Apple's Twiggy Disks ] ]

References