DDR-RAM: Single vs. Double sided

I was looking into more RAM, I have a 256mb stick of PC2100 now. I was looking for some, and found that there was both double sided and single sided sticks. The double sided was a lot more money. Both had the same amount of RAM, though. So, what IS the difference?? Also, I currently have Kingston RAM, and by looking at it, it is double sided. So would it be compatable with a different, faster brand that is single sided? And is this single sided RAM like the old SIMM's, where you need 2 of em to work, just like RDRAM is also??

Here is the site a found the RAM on, but it has since been updated (its Canadian, too:) ) http://www.e-compuvision.com/index.asp?section1=Memory

Also, I have a Shuttle AK31Rev. 3.1 mobo, with support for up to 4 1gb sticks of RAM. It uses the KT266A chipset, not KT333, which I know supports PC2100.

Thanks all

just a guess, but i would say that it is smaller memory spread out on both sides for the same total, but cooler...:confused: