Matching new RAM to old RAM: There are several things you must consider when adding RAM to your computer. The new RAM must match the old in several aspects. The most significant are: Parity. Parity RAM cannot be mixed with non-parity RAM. Either it's all parity, or all non-parity, but not mixed. Parity memory modules (and ECC memory modules) have a chip count divisible by 3. Non-parity modules have a chip count that is not divisible by 3. Also, you cannot mix parity RAM chips which use different parity (i.e. you cannot mix even-parity RAM with odd-parity RAM). Type of RAM, such as EDO, FPRAM, SDRAM, RDRAM, etc. Speed in nanoseconds (ns). This does not actually have to be identical to the old RAM's rating, but it must be fast enough to keep up with the CPU. The allowable ns rating is determined by the CPU speed. It should be noted that problems may result from mixing RAM speeds, or they may not. Although it is possible that it will go without problems, it's really a matter of chance, and to be on the safe side you should try to match speeds among all RAM modules exactly. DIMMs or SIMMS. This will depend on what kind of slots your motherboard has. Keep in mind that SIMMs must be installed in pairs, while DIMMs can be installed singly. Voltage. This, again, is determined by the motherboard (and type of RAM). According to specifications, all SDRAM must be 3.3 volts. Maximum per-module memory size. Once again, depends on the motherboard and how big a module it can take. Some motherboard won't accept a module larger than 32 MB, for example, while others have a limit of 64 MB.