The OS/2 Museum recently came into possession of what may be the first adapter with support for two IDE channels… sort of.

The adapter was made by Plus Development Corporation, a subsidiary of the disk maker Quantum. This particular specimen was manufactured in 1989, though its BIOS has a 1988 copyright.

The adapter is quite obscure for something made by a well known company. I could not find any information about it whatsoever. The only public reference to its existence is its FCC ID, EU95T8IMPULSE80-2 (note that Plus Impulse was a brand name under which some Quantum drives were sold).

There is one quite remarkable thing about the Plus Development adapter. It is entirely self-configuring. There is in fact no way at all to change the disk configuration, and the adapter does not use any information from the system BIOS (the system BIOS must not be used for disks attached to the Plus Development adapter, otherwise the machine will see the same disk twice).

It still escapes me what this adapter was really intended for. Users who needed more than two hard disks probably weren’t going to use the BIOS to access them. Most likely they’d run NetWare, SCO UNIX, OS/2, or something similar. But given the way the adapter works, the OS would need to use a driver which understands the custom control register that switches between IDE channels.

Read more in the interesting post on the OS/2 Museum blog.