Double data rate

When operating at a high bandwidth, signal integrity limitations constrain the clock frequency.

This technique has been used for microprocessor front-side busses, Ultra-3 SCSI, expansion buses (AGP, PCI-X[4]), graphics memory (GDDR), main memory (both RDRAM and DDR1 through DDR5), and the HyperTransport bus on AMD's Athlon 64 processors.

It is more recently being used for other systems with high data transfer speed requirements – as an example, for the output of analog-to-digital converters (ADCs).

The two technologies are independent of each other and many motherboards use both, by using DDR memory in a dual channel configuration.

Technically, the hertz is a unit of cycles per second, but many people refer to the number of transfers per second.

A comparison between single data rate , double data rate, and quad data rate . The dots are where data transfers take place, measured in millions of transfers per second (MT/s).