, when referring to computer
systems, is simply how many times per clock cycle
data is being transmitted. Early types of system memory (RAM
), such as SDRAM
, transmitted data on only the peaks of the cycles. With the advent of double data rate synchronous dynamic RAM
or DDR SDRAM
, the data was transmitted on both the peak and the trough of the cycle. However, quad-pumping has been used for a while for the front side bus
(FSB) of a computer system. This works by transmitting data at the peak, trough, and zero of each cycle. Intel computer systems (and others) use this technology to reach effective FSB speeds of 1066 MHz, even though the true FSB speed is only 266 MHz. A multiplier
in the CPU then multiplies the true FSB speed by a factor in order to get the CPU speed.
Example: A Core 2 Duo E6600 processor is listed as 2.4 GHz with a 1066 MHz FSB. The FSB is known to be quad-pumped, so its true frequency is 266 MHz. Therefore, the CPU multiplier is 9×. The DDR2 RAM that it is compatible with is known to be double-pumped, so to run the system synchronously (see Front side bus) the type of RAM that is appropriate is double 266 MHz, or DDR2-533.
See further explanation of these concepts with some illustrations at OEM PC World