Double Data Fee Synchronous Dynamic Random-Access Memory (DDR SDRAM) is a sort of synchronous dynamic random-entry memory (SDRAM) extensively utilized in computers and other electronic gadgets. It improves on earlier SDRAM technology by transferring data on both the rising and falling edges of the clock sign, successfully doubling the information rate without growing the clock frequency. This system, referred to as double information price (DDR), allows for increased memory bandwidth while sustaining decrease power consumption and lowered sign interference. DDR SDRAM was first introduced in the late nineties and is generally known as DDR1 to distinguish it from later generations. It has been succeeded by DDR2 SDRAM, DDR3 SDRAM, DDR4 SDRAM, and DDR5 SDRAM, each offering further enhancements in velocity, capacity, and effectivity. These generations usually are not backward or Memory Wave forward appropriate, that means memory modules from different DDR versions cannot be used interchangeably on the same motherboard. DDR SDRAM typically transfers sixty four bits of data at a time.

Its efficient switch charge is calculated by multiplying the memory bus clock pace by two (for double knowledge fee), then by the width of the data bus (sixty four bits), and dividing by eight to transform bits to bytes. For instance, a DDR module with a one hundred MHz bus clock has a peak transfer price of 1600 megabytes per second (MB/s). In the late 1980s IBM had built DRAMs utilizing a twin-edge clocking feature and introduced their results at the Worldwide Strong-State Circuits Convention in 1990. Nevertheless, it was commonplace DRAM, not SDRAM. Hyundai Electronics (now SK Hynix) the identical year. The event of DDR started in 1996, before its specification was finalized by JEDEC in June 2000 (JESD79). JEDEC has set requirements for the info rates of DDR SDRAM, divided into two components. The first specification is for Memory Wave Protocol chips, and the second is for memory modules. To increase memory capacity and bandwidth, chips are combined on a module.

For instance, the 64-bit knowledge bus for DIMM requires eight 8-bit chips, addressed in parallel. Multiple chips with common deal with traces are called a memory rank. The time period was introduced to keep away from confusion with chip internal rows and banks. A memory module could bear a couple of rank. The term sides would even be confusing as a result of it incorrectly suggests the physical placement of chips on the module. The chip choose sign is used to situation commands to particular rank. Adding modules to the only memory bus creates extra electrical load on its drivers. To mitigate the ensuing bus signaling price drop and overcome the memory bottleneck, new chipsets employ the multi-channel structure. Notice: All items listed above are specified by JEDEC as JESD79F. All RAM knowledge rates in-between or above these listed specifications are usually not standardized by JEDEC - usually they're simply manufacturer optimizations using tighter tolerances or overvolted chips.
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The bundle sizes during which DDR SDRAM is manufactured are additionally standardized by JEDEC. There isn't any architectural distinction between DDR SDRAM modules. Modules are as a substitute designed to run at completely different clock frequencies: for Memory Wave Protocol instance, a Pc-1600 module is designed to run at 100 MHz, and a Computer-2100 is designed to run at 133 MHz. A module's clock pace designates the info charge at which it is assured to perform, hence it's assured to run at lower (underclocking) and may possibly run at higher (overclocking) clock charges than those for which it was made. DDR SDRAM modules for Memory Wave desktop computer systems, dual in-line memory modules (DIMMs), have 184 pins (as opposed to 168 pins on SDRAM, or 240 pins on DDR2 SDRAM), and may be differentiated from SDRAM DIMMs by the number of notches (DDR SDRAM has one, SDRAM has two). DDR SDRAM for notebook computer systems, SO-DIMMs, have 200 pins, which is similar variety of pins as DDR2 SO-DIMMs.

These two specs are notched very equally and care should be taken throughout insertion if unsure of a appropriate match. Most DDR SDRAM operates at a voltage of 2.5 V, in comparison with 3.3 V for SDRAM. This could considerably reduce power consumption. JEDEC Customary No. 21-C defines three potential working voltages for 184 pin DDR, as identified by the important thing notch position relative to its centreline. Web page 4.5.10-7 defines 2.5V (left), 1.8V (centre), TBD (right), whereas web page 4.20.5-40 nominates 3.3V for the precise notch place. The orientation of the module for figuring out the important thing notch place is with fifty two contact positions to the left and forty contact positions to the right. Growing the operating voltage slightly can enhance most pace but at the fee of upper power dissipation and heating, and at the danger of malfunctioning or damage. Module and chip characteristics are inherently linked. Complete module capacity is a product of one chip's capability and the number of chips.