Should memory cards match? For example, let's say you have 768 MB RAM installed in your computer (one being 256 and the other 512). Isn't that wrong? And, if they don't match, what effect does this have on the PC's performance?
I dont see any problem with it. Its just one of those things where we are used to having things even and then as soon as there not we start thinking that there must be something wrong with doing it uneven. That and the RAM makes would much rather you buy 2 512 sticks then 1 512 and a 256 because they make more money that way.
The memory dimms do not have to match, not in speed nor cas latency etc, you may put whatever you wish in the slots. There are a few exceptions to this however. First, if you are running Dual Channel memory, then you will need identical Dual Channel memory dimms. Also, on some boards, they have problems with you running 2 regular dimms in dual channel slots, and will try and clock them to dual channel, however, this is an entirely separate problem. As it stands there are no conflicts with putting all sorts of different memory in most systems.