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The (non-SCSI) Hard Disk 20 does not work with the Macintosh SE/30. The Macintosh SE/30 has the same logic board and ROM as the Macintosh IIx, which does not support the Hard Disk 20. Therefore, the code to support the drive is not included in the ROM of the Macintosh SE/30.
So much for floppyEmu HDs to move data quickly onto a SE/30.