Quote from the web page:
"approximately twice as fast as 2HD mode because of the higher rotation speed in 2HD mode. "
The rotation speed is the same in 2DD and 2HD on a normal pc drive (300 rpm). AFAIK The only drives that have different speeds for DD and HD, are Amiga specific HD drives (Chinon FB-357A and FZ-357A). These drives run at half the speed in HD mode (150 rpm, because Paula can't handle more...). This issue is the biggest problem when it comes to converting a PC HD drive to Amiga HD. You will somehow have to make the drive drop to half speed when reading/writing HD disks. Look on aminet for more details, I know there's at least one file detailing these problems.
another quote:
"I think it would be interesting to discuss the possibility of building an adaptor that would fit on the ribbon cable to convert a PC floppy drive into an Amiga floppy drive. I believe that in order to get the adaptor to work on any PC floppy drive would require more expertise than I have and may be cost prohibitive"
Such a device more or less already exists, it's called Kylwalda.
Anyway, thanks for a very informative page. I might be having a look on the pile of old fdd's I've got lying around...
-Paul
