PC2 6400 = DDR2 800MHZ (Compatible with DDR2 667MHZ, DDR2 533MHZ). Speed: DDR2 800MHz. PC2 5300 = DDR2 667MHZ (Compatible with DDR2 533MHZ). PC2 4200 = DDR2 533MHZ. PC2 8500 = DDR2 1066MHZ. DDR2 for Desktop=240 pins.
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