Memory problems. How to define 64 or 128-bit technology ?

Svetik

I have MS-6183 mainboard with 128 MB 100 MHz SDRAM. I decided to increase size of RAM and bought new 256 PC100 memory card from Viking components (PC10032x64CL3-88). But computer doesn't see this card at all. I tried different slots, it didn't help. Memory card is all right, I tried it with different PC and it worked all right. I tried another card, which is 256 SDR100MHz-0305, and computer didn't see it too. However, it is written in MS-6183 manual, that this board supports 256 MB module and maximum memory size is 512MB.
I asked manufacturer this question. They answered me:
"With regard to your concern, this mainboard supports a maximum memory size of 256MB(64-bit technology) or 512MB(128-bit technology for SDRAM: It provides two 168-pin unbuffered DIMMs (Double In-Line Memory Module) sockets".
Does anybody know how to define which technology is the memory module (64bit or 128bit)? What is unbuffered DIMMs? And where can I buy this stuff?
Thank you very much,
Svetlana

Mattjimf

your best bet is to go to http://www.crucial.com/uk/systemscanner/ and download the bit of software, this will tell you exactly the type of memory you need.