DDR stands for Double Date Rate and that means it doubles the bandwidth of the memory by transferring data twice as fast on both the rising and falling of the clock cycle. 

CAS stands for Column Access Select or Column Access Strobe and that essentially means the number of cycles for the memory to get information and then process that information. Also keep in mind that a lower CAS is much better than a higher CAS, so try and keep CAS as low as possible when overclocking. 

This memory is also Dual Channel which means better overall memory bandwidth resulting in superior performance. In order to benefit from this technology you will need to have a dual channel motherboard. Non-dual channel motherboards do not have two fully independent 64-bit memory controllers, but dual channel boards do which means they have a 128-bit memory interface. Now they can be installed singly but obviously performance will be much less at the same MHz.

Please remember that this memory is DDR2 and it does differ from DDR memory in a number of ways. The following explanation below goes over the general difference. It does not take into account some of the fast DDR/DDR2 memory on the market, but is designed to help you distinguish between the two:

To begin, the maximum Data Rate is different (400MHz for DDR vs. 667MHz for DDR2), Bus Frequency (200MHz vs. 333MHz), DRAM Frequency (200MHz vs. 166MHz), Package Type (TSOP-II vs. FBGA), Voltage (~2.5 vs. 1.8), Prefetch Size (2 bits vs. 4 bits) and a CAS Latency (which varies quite a bit but in general 2.5 for DDR vs. 4 for DDR2 memory). The on-die termination is different as well. To eliminate signal noise, DDR uses transistors that are on the motherboard whereas for DDR2 it�s on each memory chip. The Off Chip Driver Calibration on DDR2 memory also increases signal integrity.

While 240-pin DDR2, 184-pin DDR and the older style 168-pin DIMM memory are all approximately the same size, the 240-pin DIMMs and 184-pin DIMMs have only one notch within the row of pins. The notch in a 240-pin DDR2 DIMM is slightly more toward the center of the module. Please keep in mind that DD2 memory is not backward compatible and will only fit motherboards specifically designed for it.

Now, what�s the bottom line on this new DDR2 memory? Is it faster than DDR at the same speed? The short answer is, currently, not really. However, remember DDR2 is fairly new to the market so it will take some time for hardware and software companies to fully utilize its overclockability, superior performance and bandwidth. One notable improvement in DDR2 memory is the tighter memory timing. That's crucial for better performance.

Details Specifications:
Speed: PC2 4200 or 533 DDR2 (267MHz)
Size: 512MB Module (PN: OCZ2533512ELGEGXT) and
        1GB Module (PN: OCZ25331024ELGEGXT)
Configuration: 64MB x 8 / 128MB x 8
Chips: X42A120840C-37 IC
Latency: 4-4-4-12 (CAS-TRCD-TRP-TRAS)
Package Type: 240 DIMM
Heat Spreader: Gold Layered XTC Heatspreader
Voltage: 1.9