DDR Ram

DDR SDRAM (double-data-rate SDRAM): DDR SDRAM is similar to SDRAM, but it transfers data on the rising and falling edges of the system clock, theoretically doubling the speed of SDRAM. Though DDR SDRAM was originally developed for graphics cards, desktop PC manufacturers now use it as system memory as well.

DDR SDRAM is not compatible with older systems. If you want to upgrade your RAM to DDR SDRAM, your PC's motherboard needs to support 184-pin DIMM slots, and your processor must be fast enough to handle the extra bandwidth is recommended to run DDR pc3200 otherwise called DDR400mhz); otherwise, all that speed just goes to waste. PC2700 - 2.6GB/s bandwidth (8 x 166 x 2), runs at DDR-333mhz and PC3200 - 3.2GB/s bandwidth (8 x 200 x 2), runs at DDR-400mhz.

CAS number in the memory rating

CAS (Column Access Strobe) latency: CAL Latency usually has the most impact on memory performance. A common marketing term attached to SDRAM modules is either "CAS2" or "CAS3". Unfortunately, this is a bit misleading, as they should be referred to as CL2 or CL3, since they refer to CAS Latency timings (2 clocks vs. 3 clocks). A CAS latency of 2 clocks is currently very good. Each is described with a rating number, where lower numbers are better. The rating is also dependant on the front side bus speed of your motherboard so the rating may rise on higher speeds.

ECC

Error Correcting Code or ECC memory includes special circuitry for testing the accuracy of data as it passes in and out of memory. That makes this a very popular choice for servers and high-end workstations.

Enhanced Latency

Enhanced Latency: EL refers to reduce latency cycles implying that these memory modules run at lower latencies than standard memory. Enhanced Latency DDR components increase the overall memory bandwidth at any given clock speed by lowering the amount of cycles required to initiate an operation.