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In computing
Computing

Computing is usually defined as the activity of using and developing computer technology, computer hardware and computer software. It is the computer-specific part of information technology....
, a computer bus
Computer bus

In computer architecture, a bus is a subsystem that transfers data between computer components inside a computer or between computers. Each bus defines its set of connectors to physically plug devices, cards or cables together....
 operating with double data rate transfers data on both the rising and falling edges of the clock signal
Clock signal

In electronics and especially Synchronous logic digital circuits, a clock signal is a Signalling used to coordinate the actions of two or more Electronic circuit....
. This is also known as double pumped, dual-pumped, and double transition.

The simplest way to design a clocked electronic circuit
Electronic circuit

An electronic circuit is a closed path formed by the interconnection of electronic components through which an electric current can flow. The electronic circuits may be physically constructed using any number of methods....
 is to make it perform one transfer per full cycle (rise and fall) of a clock signal
Clock signal

In electronics and especially Synchronous logic digital circuits, a clock signal is a Signalling used to coordinate the actions of two or more Electronic circuit....
. This, however, requires that the clock signal changes twice per transfer, while the data lines change at most once per transfer.






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In computing
Computing

Computing is usually defined as the activity of using and developing computer technology, computer hardware and computer software. It is the computer-specific part of information technology....
, a computer bus
Computer bus

In computer architecture, a bus is a subsystem that transfers data between computer components inside a computer or between computers. Each bus defines its set of connectors to physically plug devices, cards or cables together....
 operating with double data rate transfers data on both the rising and falling edges of the clock signal
Clock signal

In electronics and especially Synchronous logic digital circuits, a clock signal is a Signalling used to coordinate the actions of two or more Electronic circuit....
. This is also known as double pumped, dual-pumped, and double transition.

The simplest way to design a clocked electronic circuit
Electronic circuit

An electronic circuit is a closed path formed by the interconnection of electronic components through which an electric current can flow. The electronic circuits may be physically constructed using any number of methods....
 is to make it perform one transfer per full cycle (rise and fall) of a clock signal
Clock signal

In electronics and especially Synchronous logic digital circuits, a clock signal is a Signalling used to coordinate the actions of two or more Electronic circuit....
. 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
Signal integrity

Signal integrity or SI is a measure of the quality of an electrical signal. In digital electronics, a stream of binary values is represented by a voltage waveform....
 limitations constrain the clock frequency
Frequency

Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency....
. By using both edges of the clock, the data signals operate at the same limiting frequency, doubling the data transmission rate.

This technique has been used for microprocessor front side bus
Front side bus

In personal computers, the Front Side Bus is the bus that carries data between the central processing unit and the Northbridge .Depending on the processor used, some computers may also have a back side bus that connects the CPU to the CPU cache....
ses, Ultra-3 SCSI
SCSI

Small Computer System Interface, or SCSI , is a set of standards for physically connecting and transferring data between computers and peripheral devices....
, the AGP
Accelerated Graphics Port

The Accelerated Graphics Port is a high-speed point-to-point channel for attaching a :Category:Graphics cards to a computer's motherboard, primarily to assist in the acceleration of 3D computer graphics....
 bus, DDR SDRAM
DDR SDRAM

DDR SDRAM is a class of memory integrated circuits used in computers. It achieves nearly twice the bandwidth of the preceding "single data rate" SDRAM by double data rate without increasing the clock frequency....
, and the HyperTransport
HyperTransport

HyperTransport , formerly known as Lightning Data Transport , is a bidirectional serial/parallel high-bandwidth, Memory latency Point-to-point that was introduced on April 2 2001....
 bus on AMD's Athlon 64
Athlon 64

The Athlon 64 is an eighth-generation, AMD64-architecture microprocessor produced by AMD, released on September 23, 2003. It is the third processor to bear the name Athlon, and the immediate successor to the Athlon XP....
 processors.

An alternative to double or quad pumping is to make the link self-clocking
Self-clocking signal

In telecommunications and electronics, a self-clocking signal is one that can be decoded without the need for a separate clock signal or other source of synchronization....
. This tactic was chosen by InfiniBand
InfiniBand

InfiniBand is a switched fabric communications link primarily used in high-performance computing. Its features include quality of service and failover, and it is designed to be scalability....
 and PCI Express
PCI Express

Peripheral Component Interconnect Express , officially abbreviated as PCIe, is a computer expansion card standard designed to replace the older PCI Local Bus, PCI-X, and Accelerated Graphics Port standards....
.

Describing the bandwidth of a double-pumped bus can be confusing. Each clock edge is referred to as a "beat
Beat (music)

A beat is the basic time unit within much Western music; for example, each tick sounded by a metronome would correspond to a beat. More technically, "the beat is the pulse of the mensural level", also known as the beat level, the meter level at which pulses are heard as the basic unit?"the denominator of the time signature,"...
", with two beats (one upbeat and one downbeat
Downbeat

In music performance and music theory, the downbeat is the first beat of a Bar in music, the impulse that occurs at the beginning of a bar in measured music....
) per cycle. Technically, the Hertz
Hertz

The hertz is a measure of frequency per unit of time, or the number of list of cycles per second. It is the SI base unit of frequency in the International System of Units , and is used worldwide in both general-purpose and scientific contexts....
 is a unit of cycles per second, but many people refer to the number of transfers per second. Careful usage generally talks about "500 MHz, double data rate" or "1000 MT/s", but people will refer casually to a "1000 MHz bus", even though no signal cycles faster than 500 MHz.

DDR SDRAM popularized the technique of referring to the bus bandwidth in megabytes per second, the product of the transfer rate and the bus width in bytes. DDR SDRAM operating with a 100 MHz clock is called DDR-200 (after its 200 MT/s data transfer rate), and a 64 bit (8 byte) wide DIMM
DIMM

A DIMM, or dual in-line memory module, comprises a series of dynamic random access memory integrated circuits. These modules are mounted on a printed circuit board and designed for use in personal computers, workstations and Server s....
 operated at that data rate is called PC-1600, after its 1600 MB/s peak (theoretical) bandwidth. Likewise, 800 MHz clock DDR3-1600 is called PC3-12800.

Note that DDR SDRAM only uses double-data-rate signalling
Signalling (telecommunications)

In telecommunication, signalling or signaling has the following meanings:*The use of signals for controlling communications.*In a telecommunications network, the information exchange concerning the establishment and control of a Telecommunication circuit and the management of the network, in contrast to User information transfer....
 on the data lines. Address and control signals are still sent to the DRAM once per clock cycle, and timing parameters such as CAS latency
CAS Latency

CAS RAM latency is the delay time which elapses between the moment a memory controller tells the memory module to access a particular column in a selected row, and the moment the data from the given array location is available on the module's output pins....
 are specified in clock cycles.

See also

  • DDR SDRAM
    DDR SDRAM

    DDR SDRAM is a class of memory integrated circuits used in computers. It achieves nearly twice the bandwidth of the preceding "single data rate" SDRAM by double data rate without increasing the clock frequency....
    , DDR2 SDRAM
    DDR2 SDRAM

    DDR2 SDRAM or Double Data Rate two synchronous dynamic random access memory is a random access memory technology used in electronic engineering for high bandwidth storage of the working data of a computer or other digital electronics device....
    , and DDR3 SDRAM
    DDR3 SDRAM

    In electronic engineering, DDR3 SDRAM or Double data rate three synchronous dynamic random access memory is a random access memory interface technology used for high bandwidth storage of the working data of a computer or other digital electronics devices....
     which all use DDR signalling
  • Quad data rate
    Quad Data Rate

    Quad data rate is a communication signaling technique wherein data is transmitted at four points in the clock cycle: on the rising and falling edges, and at two intermediate points between them....
  • Pumping (computer systems)
    Pumping (computer systems)

    Pumping, when referring to computer systems, is simply how many times per clock cycle data is being transmitted. Early types of system memory , such as SDRAM, transmitted data on only the peaks of the cycles....