I've got an old computer from a friend of mine that does not use it anymore i order to use it like a test server. Now, I'd like to upgrade it, by adding to it some RAM.
Wondering about how to know what kind of RAM should I add: SDR or DDR?
Head on over to crucial.com's website and run their Crucial System Scanner tool.
This will tell you exactly what memory your computer uses, how many slots there are and exactly what memory will be compatible.
They even offer a money back guarantee if you purchase through their website using their scanner and it turns out to be incompatible.
You might want to install CPU-Z from CPUID.
Here's what you see (with mine, that is):