Can I use two or more different types of memory modules at a time?
This is depending on the way in which you want to mix-up the different memory modules.
We have to pay attention that the RAM memory modules are identical. Theoretically you could use RAM memory modules with different specifications simultaneously but this is not recommended. If we are using a RAM memory module with a slower pulsing and latency and a RAM memory module with a higher pulsing and with a higher latency the operating system will generally work with the pulsing and latency of the slower memory module. If a DDR333 memory module is already installed in the PC and if you want to additionally install a DDR400 memory module in the PC, this is generally possible but the two memory modules will then work with the pulse frequency of 166MHz, which corresponds to the pulse frequency of the DDR333 memory module.
Please make sure that the RAM memory modules are of the same brand and specification. If you do not know the brand of your RAM memory module please use an identification tool, such as Aida32, in order to read out the brand of your RAM memory module.
Warning: You cannot use two different types of RAM memory modules, such as for instance a DDR RAM memory module together with an SDR RAM memory module or an SDR RAM memory module together with an EDO RAM memory module.