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Tom's Ultimate RAM Speed Tests

DDR2 Speeds

Standard nameMemory clockCycle timeI/O Bus clockData transfers per secondModule namePeak transfer rate
DDR2-400100 MHz10 ns200 MHz400 MillionPC2-32003200 MB/s
DDR2-533133 MHz7.5 ns266 MHz533 MillionPC2-4200PC2-430014266 MB/s
DDR2-667166 MHz6 ns333 MHz667 MillionPC2-5300PC2-540015333 MB/s
DDR2-800200 MHz5 ns400 MHz800 MillionPC2-64006400 MB/s
DDR2-1066266 MHz3.75 ns533 MHz1066 MillionPC2-85008533 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 nameMemory clockCycle timeI/O Bus clockData transfers per secondModule namePeak transfer rate
DDR3-800100 MHz10 ns400 MHz800 MillionPC3-64006400 MB/s
DDR3-1066133 MHz7.5 ns533 MHz1066 MillionPC3-85008533 MB/s
DDR3-1333166 MHz6 ns667 MHz1333 MillionPC3-1060010667 MB/s[4]
DDR3-1600200 MHz5 ns800 MHz1600 MillionPC3-1280012800 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.