PC2 6400 = DDR2 800MHZ (Compatible with DDR2 667MHZ, DDR2 533MHZ). Total Capacity:2GB;Speed: DDR2 800MHz (PC2-6400U). PC2 5300 = DDR2 667MHZ (Compatible with DDR2 533MHZ). PC2 4200 = DDR2 533MHZ. PC2 8500 = DDR2 1066MHZ.
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