The answer to your question is hard to explain any other way. When buying RAM, the lower the Latency and lower the voltage required to run at those advertised latencys and data transfer rates (speed) the better quality the DIMMs should be. So, 4-4-4-12 capable is more desirable than 5-5-5-15 for example, but for all intents and purposes, you have to really know yoiur system's performance well and first hand to tell much difference there. HTH.