The speed of DDR is usually expressed in terms of it's "effective data rate", which is twice its actual clock speed. PC3200 memory, or DDR400, or 400MHz DDR, is not running at 400MHz, it is running at 200MHz. The fact that it accomplishes two data transfers per clock cycle gives it nearly the same bandwidth as SDR SDRAM running at 400MHz, but DDR400 is indeed still running at 200MHz.

Actual clock speed/effective transfer rate

100/200MHz => DDR200 or PC1600 DDR
133/266MHz => DDR266 or PC2100 DDR
166/333MHz => DDR333 or PC2700 DDR
185/370MHz => DDR370 or PC3000 DDR
200/400MHz => DDR400 or PC3200 DDR
217/433MHz => DDR433 or PC3500 DDR
233/466MHz => DDR466 or PC3700 DDR
250/500MHz => DDR500 or PC4000 DDR
267/533MHz => DDR533 or PC4200 DDR
283/566MHz => DDR566 or PC4500 DDR

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by Exit edited by FastEddie
last modified: 2004-02-08 18:40:57