|First, when you install different types of memory (assuming all types are compatible) the system will run all to the speed of the slowest. Some times the memory is too far apart and will not run together though. When this happens, try switching the sticks which sometimes works and sometimes does not. Try running each type separately to make sure both are compatible and working and not just a bad stick.|
Second, All that said, it is best to run the same or at least equivalent memory sticks in any system. You need to match Voltage, Speed, and Latency to run well. That said, for optimal dual channel support you should run memory sticks as matched pairs that are purchased in a twin package.
Third, you can remove memory sticks and read the info right off the labels that are on them or you can go to www.crucial.com and let their app scan your system and recommend memory for your system, even if you do not purchase from them, the info on the recommended memory will usually be optimal for your system.
You have to be a little bit crazy to keep you from going insane.