I dug this up... anyone want it? make an offer.
What the heck is a slim card?
Looks like some sort of PDS or NuBus expansion device...but I've never, ever heard of it.
I think its a combonation of a dongle and some kind of CF type storage.. but i've never heard anything about it, so thats just my guess.
That's the same as an LC PDS connector (DIN 96), suggesting something education-market oriented. I wonder if there might have also been an OS card for the other slot, to allow a HD-less LC-class Mac (eg: in a school setting) to boot to unmodifiable startup disk. Just speculation on my part you understand.
There was probably more to it, almost certainly a mounting bracket, even perhaps a bezel to allow allow swapping cards without opening the case. Those ribbon cables however seem rather short to allow mounting for the holder's slots to reach the front of an LC . . .
Actually, that stirs a memory...a long time ago, my local public library got a whole bunch of LC 550s for public use for catalog lookups. Being a nerd, I asked about them, and the librarian said that they weren't normal Macs--she said that they were "d-Macs." I never bothered to look further into it, but I'd be willing to bet that these cards were what they used.
The card must slide in and out of the back of the machine, because I remember that the library Macs didn't look any different from the front, e.g. the floppy drive was still there and there weren't any extra slots.
SLIM cards were supposed to be an alternative media for the Macintosh portable. Those two drives plugged into the expansion connector and would sit above the floppy drive.
ROM support for these was implemented and shipped, so if you plug this into a Portable, it might just work. AFAIK, one reason they were cancelled is that they didn't pass the shake testing. That is, the drive tried to hold onto the card, but it could be shaken out of it fairly easily, so the assumption the OS had that it controlled the ejection of a drive didn't hold true.
Funny story-- there was a big flap at the time about radio personality Chuck Farnham having gotten a hold of a copy of the Mac Portable Engineering Requirements Specification (dumpster diving? social engineering? I never heard the whole story). He had taken the page from the spec that showed sample card artwork and screened it onto shirts seen at MacWorld Expo that year.