http://bitsavers.trailing-edge.com/pdf/apple/disk/hd20/

This information was already talked about some what… and has already been seen by Mr. BMOW him self…

https://mac68k.info/forums/thread.jspa?threadID=252&start=60&tstart=0

All i can say is MY GOD WHAT A MASSIVELY COMPLEX/PROPRIETARY WAY TO ATTACH A HD TO YOUR MAC!

(look at doc's) Everything is special… Special HD-PCB, Special interface Board, Special Software in rom….

If anyone has any info they would like to add about this please feel free.

From BMOW:

HD20 is a totally different thing, and other than using the same DB-19 connector it has nothing at all in common with the floppy drive, so it might need a total re-write to do it.

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He's done a boat load of work on this asis!

Also :

According to http://www.mac512.com/macwebpages/hd20.htm, there are only six Macs with HD20 support in ROM - the Mac Portable was the last. Too bad it's not compatible with more models.

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With only 6 macs with support for this… might not even be worth the time?

i dunno it would be a great option for the mac portable!!!!!!!!!!!!!!!!! Something other then making one of those annoying 34 pin to 50 pin adaptors…

there is 2 floppy ports in there too