Upgrading A Mac II Floppy To A 1.4 meg (SuperDrive)
The "Superdrive" kit for the Mac II consists of:
1) SWIM chip, which replaces the IWM chip, and provides support for the Superdrive's MFM format (1.44M) in addition to its GCR format (800K), and
2) Firmware chips (four) which replaces the standard firmware, and provides support for the SWIM chip. There are two versions of this firmware, with the first simply provides the SWIM chip support and the second which also fixes a
The combination of (1) and (2) essentially makes a Mac II motherboard into a IIx motherboard.
Apple has not stocked the Superdrive kit for the Mac II for at least five years.
In some machines, specifically some very old machines which are not capable of supporting the Superdrive in 800K mode, a Superdrive may still be used, although in 800K mode only, by substituting a special "yellow striped" floppy cable for the normal "red stripped" floppy cable.
This yellow-striped cable deletes certain signal lines that, if wired, confuses the Superdrive.
A total of four signal lines are not used in the Superdrive. The yellow-striped cable deletes the only line that is causing the confusion. The other three lines are not wired on the Superdrive's cable connector.
Apparently, substitution of the SWIM chip for the IWM results in a Mac II results in all four signals automatically being deleted, thereby obviating the need for the yellow-striped floppy cable.
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