They're marked KTD-PC100X72RC3/256I 9852222-002.A00 so they should be made by Kingston but I've been unable to find any datasheet about them.
I think KTD is the prefix Kingston used for memory they made for Dell. I know KTC is Compaq and KTM is IBM.
This page
http://www.allquests.com/question/1923128/upd … redge-1300.html
if it's accurate, lists that part number for Dell PowerEdge 1300, 2300, 4300, 4350. But really it would work on anything with an appropriate chipset.
A few years ago I bought a bulk listing of about 100-150 memory modules, most of them were 36-chip 256MB PC100 Registered ECC. Many of them look like these. Some have dual PCBs soldered together, some are connected by ribbon cables (!) but usually the chips are directly piggybacked on each other (which is hard to tell without looking close).
I doubt any of the super 7 chipsets support registered memory, but I'm not sure.
I imagine these were mostly used with 440BX/440GX workstations and servers, but a 440BX desktop will work just as well. That's what they would be most useful with. I think a VIA KT133 (Athlon) or 694X (P3) chipset will also take them but I'm not sure. Being PC100 reduces their usefulness with those.
At the time these were made, I'm guessing they had to use 4-bit chips to get the size they wanted. The use of 4-bit chips is JEDEC legit with registered memory and it's allowed by the 440BX and 440GX specs, and probably any other registered memory chipset. However, it's not allowed for unbuffered memory, and there was some shoddy no-name memory that broke that rule.
Yours is registered though, so it's not doing anything wrong other than not being what the seller advertised.
My 440GX HP Kayak actually requires stacked memory to achieve 512MB per DIMM. It took me years to figure that out. I ordered a module from Crucial which was guaranteed compatible, but it didn't work. It was a typical 18-chip module with 8-bit chips. It met the chipset specs but even the latest version of HPs broke-ass BIOS wouldn't take it. It would count the memory at POST, but as soon as it handed off to the operating system, it would give an ECC error. A replacement did the same thing.
Because of the BIOS, it HAD to have the older modules with 36 4-bit chips. And those were too tall, so I mangled the insides to make one of them fit. I couldn't figure out what HP was thinking.
Much later I finally realized the existence of these stacked modules that aren't double-tall. That's the only type of 512MB module that will both work and physically fit.