User`s guide

shifted to hard drives, CD-ROM, and flopticals. Few Mac owners have use for the
external 3.5" drive any more; if they have not yet discarded their external 3.5"
drive, it is now in storage.
MAC AND APPLE II 3.5" DRIVES: SIMILARITIES/DIFFERENCES
The basic Sony 3.5" mechanism is shared by Mac and Apple II. It stores
800K of data on a two-sided disk. Unlike the IBM version with its constant
rotational speed, Mac/Apple II drives maintain constant head velocity by varying
the rotational speed as the head assembly approaches towards or moves away from
the disk hub. Mac and Apple II drives differ in their track sectoring
arrangements, so disks cannot be read directly without special translational
software. The opportunity for compatible disk sh
aring was lost during development, because rival teams working on Mac/Apple II
drives went their separate ways (Steve Weyhrich, APPLE II HISTORY, Pt. 9, 1992).
The platinum 3.5" drive supplied with the IIgs is directly compatible with
the Mac, although the Mac ignores its front panel manual eject button; Mac disk
ejection is handled strictly by the desktop trash icon command. An older
version of the external Mac 3.5" drive lacks the manual eject button and, in its
casing, is plug-incompatible with Apple II. Thanks to advice provided by Ken
Watanabe, I learned that the inner mechanism is identical among all versions of
800K Mac and Apple II drives, includi
ng the internal drive mechanism in the Mac CPU. This is good news for Apple II
users who wish to transplant the abundantly available Mac mechanism into their
platinum 3.5" drive casing.
WHAT ABOUT THE APPLE UNIDISK 3.5" DRIVE?
The classic white UniDisk drive was released in 1985 as a 3.5" platform for
the IIe and IIc. This release date was 18 months prior to the introduction of
the IIgs. Disks written by the UniDisk 3.5 and Platinum 3.5 drives are fully
interchangeable; the two models differed because the earlier UniDisk 3.5 used an
intelligent microprocessor-controlled analog board to slow the data transfer
rate to match the IIe/IIc parameters. This slowdown was not needed for the
popular platinum 3.5 drive used by the
IIgs.
Can the Mac mechanism be transplanted to the UniDisk 3.5 casing? Probably
yes, but this has not yet been verified. I am reluctant tohack with the working
UniDisk 3.5's attached to my IIC's. I now seek a mechanically jammed UniDisk
3.5 drive to verify whether its life can be resurrected with a Mac transplant.
FINDING A USED MAC 3.5" DRIVE MECHANISM
The internall DSDD 800k drive mechanism can be salvaged from any mid-
vintage Mac except for early models (Mac 128, Fat Mac 512) ---- those two models
used a quaint single-sided 400k drive. Suitable models include the Mac Plus,
Mac SE, Mac II, or other Macs that have the standard DSDD 800K mechanism ---
newer Macs have incompatible high density drives. Get a genuine Mac Sony drive
mechanism, not a clone; the suitability of non-Sony clones is uncertain.
Salvaged internal drives must be removed from the Mac internal mounting
bracket --- take out the four side-mounted bolts, and slide the mechanism