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:
“The Cossack eats Poland,
Like stolen fruit;
Her last noble is ruined,
Her last poet mute:
Straight, into double band
The victors divide;
Half for freedom strike and stand;—
The astonished Muse finds thousands at her side.”
—Ralph Waldo Emerson (1803–1882)
“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)
“All of us failed to match our dreams of perfection. So I rate us on the basis of our splendid failure to do the impossible.”
—William Faulkner (1897–1962)