In computing, a computer bus operating with double data rate transfers data on both the rising and falling edges of the clock signal. This is also known as double pumped, dual-pumped, and double transition. The term toggle mode is used in the context of NAND flash memory.
The simplest way to design a clocked electronic circuit is to make it perform one transfer per full cycle (rise and fall) of a clock signal. This, however, requires that the clock signal changes twice per transfer, while the data lines change at most once per transfer. When operating at a high bandwidth, signal integrity limitations constrain the clock frequency. By using both edges of the clock, the data signals operate with the same limiting frequency, thereby doubling the data transmission rate.
This technique has been used for microprocessor front side busses, Ultra-3 SCSI, graphics RAM (the AGP bus and GDDR), main memory (both RDRAM and DDR1 through DDR4), 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 - e.g. for the output of analog-to-digital converters (ADCs).
DDR should not be confused with dual channel, in which each memory channel accesses two RAM modules simultaneously. The two technologies are independent of each other and many motherboards use both, by using DDR memory in a dual channel configuration.
An alternative to double or quad pumping is to make the link self-clocking. This tactic was chosen by InfiniBand and PCI Express.
Read more about Double Data Rate: Relation of Bandwidth and Frequency
Famous quotes containing the words double, data and/or rate:
“What happens is that, as with drugs, he needs a stronger shot each time, and women are just women. The consumption of one woman is the consumption of all. You can’t double the dose.”
—Ian Fleming (1908–1964)
“Mental health data from the 1950’s on middle-aged women showed them to be a particularly distressed group, vulnerable to depression and feelings of uselessness. This isn’t surprising. If society tells you that your main role is to be attractive to men and you are getting crow’s feet, and to be a mother to children and yours are leaving home, no wonder you are distressed.”
—Grace Baruch (20th century)
“This is the essential distinction—even opposition—between the painting and the film: the painting is composed subjectively, the film objectively. However highly we rate the function of the scenario writer—in actual practice it is rated very low—we must recognize that the film is not transposed directly and freely from the mind by means of a docile medium like paint, but must be cut piece-meal out of the lumbering material of the actual visible world.”
—Sir Herbert Read (1893–1968)