There is very little that's different between the RAM in your two links except the RAM in the first link is one SINGLE 1 GB DIMM (model PEP1G3200LL) from Patriot's Extreme Performance series (
more info here at Patriot's website ) and the RAM in your second link is a dual-channel kit model PDC1G3200LLK comprised of two 512MB DIMMs for a total of 1GB. This dual channel kit is from Patriot's dual channel series. More info on this dual-channel kit can be found
over here at Patriot's Website .
Both of your links point to Patriot-brand PC3200 RAM (also known as DDR400 ) . The "3200" indicates that the memory has a maximum theoretical bandwith of 3.2 GB/second. The DDR in DDR400 stands for
Double
Data
Rate and the "400" for the memory's effective frequency of 400MHz.
You will notice that the memory timings (tCAS, tRCD, tRP, and tRAS) are the same for both of those models of RAM at 2-3-2-5.
However, if you only use ONE of the 1GB stick of RAM on a motherboard that supports "dual channel" mode you will lose about 3-5% performance over using the PCD1G3200LLK DUAL CHANNEL kit. You will note that the price for the 1G DIMM and the dual channel kit (512MB X 2) is almost the same.
If 1 GB is the amount of memory you think you will need then under most circumstances you should opt for the dual channel kit if your motherboard supports dual channel mode; otherwise the single 1GB module leaves you the most room for expansion in the future.
Another choice for Patriot dual channel is
this Patriot PCD1G3200+XBLK dual channel memory kit. You will notice it is a little more expensive than the PCD1G3200LLK dual channel kit but it's tRCD rating is 2 instead of 3 which can enhance perfomance up to 4 percent, hence its more expensive price.
BTW, here are explanations of memory timings taken from Patriot's website:
tCL - CAS Latency (also labeled as CAS Latency Time, CAS Timing Delay) The number of clock cycles that pass from the column being addressed to the data arriving in the output register. The memory manufacturer lists the best possible setting as the CL rating.
tRCD - RAS to CAS Delay (also labeled as Active to CMD) Number of clock cycles that pass between the row address being determined and the column address being sent out. Setting this value to two clock cycles can enhance performance by up to four percent.
tRP - RAS Precharge Time (also labeled as RAS Precharge, Precharge to active) Number of clock cycles needed to precharge the circuits so that the row address can be determined.
tRAS - Row Active Time (also labeled as Active to Precharge Delay, Row Active Delay, Row Precharge Delay) Delay that results when two different rows in a memory chip are addressed one after another.
CMD - Command Rate (also labeled as CMD Rate) Number of clock cycles needed to address the memory module and the memory chip with the desired data zone. If your memory banks are full to capacity, you will have to raise this rate to two, resulting in a considerable drop in performance.
Memory timings are usually in the following order:
tCL - tRCD - tRP - tRAS - CMD
For example, our PDC1G3200LLK has a timing of 2-3-2-5-t1. This translates to the following:
tCL = 2 tRCD = 3 tRP = 2 tRAS = 5 CMD = 1