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DDR2 Speeds

Tom's Ultimate RAM Speed Tests
By
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 PC2-4200
PC2-43001
4266 MB/s
DDR2-667 166 MHz 6 ns 333 MHz 667 Million PC2-5300
PC2-54001
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

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.

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