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DDR Speed Chart
This PC rating equals . . . this mhz speed
PC 2100 DDR 266
PC 2700 DDR 333
PC 3200 DDR 400
PC 3500 DDR 433
PC 3700 DDR 466
PC 4000 DDR 500
PC 4200 DDR 533
PC 4400 DDR 550
PC 4500 DDR 566
PC 4800 DDR 600
PC 5000 DDR 625
PC 5300 DDR 667

 

DDR and DDR2

Double Data Rate Synchronous DRAM (DDR SDRAM) is an enhanced technology relative to PC100 and PC133 SDRAM DIMMs. Although they’re similar in size, DDR performs twice the operations per clock cycle.

DDR’s advantage stems from reading data on both the rising and falling edges of the clock signal, while SDRAM reads information only on the rising edge, transferring data at half the speed of DDR (i.e. – 133MHz compared to 266MHz).

DDR modules have 184 pins compared to SDRAM’s 168 pins, preventing it from fitting into a standard DIMM socket. DDR SO-DIMMs are 200pin, versus the SDRAM SO-DIMMs at 144 pin.

DDR2 raises the speed bar even past DDR. DDR2 lowers power consumption, yet increases memory speeds up to 667MHz. It almost doubles bandwidth from 6.4GB/sec to 10.6GB/sec. DDR2 also features "On-Die Termination" preventing errors at high speeds.

DDR2 is not backwards compatible with DDR and has a different "key" or notch so it cannot be used in standard DDR boards.