The HDSD board adapts the Synclavier (10/1984-6/1992) D100A high density (HD) Superfloppy controller card to the Synclavier II (6/1980-4/1984) single density (SD) and double density "shoebox" floppy disk drives. This allows the newer D100A to be a 100% drop-in replacement for the older D100 card.

While it would appear to be senseless to do such a tricky modification to use a high value still-current spec D100A in place of an obsolete D100, the reality is that the D100 was only made for a few years, is a very complex card that suffers high failure rates, and probably 80% of the few hundred made were thrown in the trash when upgraded to Superfloppy high density drives controlled by the newer D100A card. The D100A cards are always available, the D100 cards are sometimes available, sometimes not.

With this new adapter, either board can be used in an otherwise all-original Synclavier II.

The older D100 single density/double density drive controller card uses a stupid 20-pin floppy drive connection that wasn't standard to anything, ever. It was proprietary to NED and was never documented anywhere (and still isn't). This, much like the later 34-pin D24 SCSI card (there was never any such thing as 34-pin SCSI, the use of it required adapters everywhere, even inside their own system, either SLSI boards, inside all NED ATS 80mb SCSI Winchester drives and inside the black box magic adapter unit that connected the optical drives to the system, Synhouse solved this problem with the SCSI5034) or complicated and fragile adapter cables (which private techs made to avoid the cost of the black box) was probably meant to confuse people and prevent them from buying disk drives, cables, etc. from computer stores.

In 1980, a floppy drive from NED was $1,000. In 1984, a floppy drive from NED was $1,400. In 1987, a floppy drive from NED was $1,500. This pricing wasn't exactly tracking the trajectory of computer hardware prices in the 1980s.

Cards with stupid non-standard pinouts were an important part of protecting this pricing scheme.

The later D100A high density (HD) Superfloppy controller card didn't have a standard pinout, either, but at least it was 34-pin like everything else in the computer world.

The HDSD is a very small board, two of the type shown on this page can snap onto a D100A for single density/double density drive use:

The version shown in the photos uses special connectors to let it attach directly to the D100A card without the use of any other cables.

Other versions of the HDSD are also made to perform very different functions, not only with the D100A, but with the older D100 as well:

One version can connect to cables, with the board mounted, placed inline in the cable, or on a tabletop.

Another version can connect the 20-pin Synclavier II D100 floppy disk controller to a standard 34-pin flash memory-based floppy drive emulator.

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