DDR2 Speeds
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| Standard name | Memory clock | Cycle time | I/O Bus clock | Data transfers per second | Module name | Peak transfer rate |
|---|---|---|---|---|---|---|
| DDR2-400 | 100 MHz | 10 ns | 200 MHz | 400 Million | PC2-3200 | 3200 MB/s |
| DDR2-533 | 133 MHz | 7.5 ns | 266 MHz | 533 Million | PC2-4200PC2-43001 | 4266 MB/s |
| DDR2-667 | 166 MHz | 6 ns | 333 MHz | 667 Million | PC2-5300PC2-54001 | 5333 MB/s |
| DDR2-800 | 200 MHz | 5 ns | 400 MHz | 800 Million | PC2-6400 | 6400 MB/s |
| DDR2-1066 | 266 MHz | 3.75 ns | 533 MHz | 1066 Million | PC2-8500 | 8533 MB/s |
Source: Wikipedia
At this point, mainstream users should go for branded DDR2-800 memory. Quicker timings (low CL values) are favorable, but you shouldn’t fork out considerably more money, as the differences are small. DDR2-1066 is important for systems based on AMD Phenom processors, as their memory controllers can utilize the faster memory.
DDR3 Speeds
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| Standard name | Memory clock | Cycle time | I/O Bus clock | Data transfers per second | Module name | Peak transfer rate |
|---|---|---|---|---|---|---|
| DDR3-800 | 100 MHz | 10 ns | 400 MHz | 800 Million | PC3-6400 | 6400 MB/s |
| DDR3-1066 | 133 MHz | 7.5 ns | 533 MHz | 1066 Million | PC3-8500 | 8533 MB/s |
| DDR3-1333 | 166 MHz | 6 ns | 667 MHz | 1333 Million | PC3-10600 | 10667 MB/s[4] |
| DDR3-1600 | 200 MHz | 5 ns | 800 MHz | 1600 Million | PC3-12800 | 12800 MB/s |
Source: Wikipedia
At this point we recommend waiting on purchasing DDR3 memory, as most speed grades are still considerably more expensive than DDR2 RAM, without delivering better performance. Even when it comes to high capacity memory kits, you can get much cheaper deals on quad 2 GB DDR2 DIMM packages than on comparable DDR3 memory.
