Support of the serial HD-20s is not tied to System Software, but to the ROM
in the respective systems.
The following Macintosh models have support for the serial (non-SCSI) HD-20
built into ROM:
* Macintosh 512Ke
* Macintosh Plus
* Macintosh SE
* Macintosh Classic
* Macintosh IIci
* Macintosh Portable
The following Macintosh models do NOT have this support built in:
* Macintosh SE/30
* Macintosh II
* Macintosh IIx
* Macintosh IIcx
* Macintosh IIsi
* Macintosh IIfx
* Macintosh LC
For more information on the serial HD-20, see the article "Old HD20 and New
Mac SE/30".