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(Synchronous DRAM) The type of dynamic RAM memory chip that has been widely used since the mid-1990s. SDRAM eliminated wait states by dividing the chip into two cell blocks and interleaving data between them. While a bit in one block is accessed, a bit in the other is prepared for access. See dynamic RAM.

DDR (Double Data Rate)
In 2000, DDR SDRAM doubled the data transfer rate by using both the rising and falling edges of the clock cycle. The data rate of each DDR generation is faster than the previous with a six-fold increase from DDR1 to DDR4. In addition, less power is required (see table below). In order to prevent inserting the wrong DDR into the motherboard, DDR memory modules are keyed differently (for details, see memory module).

Chipsets on the motherboard may support one, two or four memory channels (triple channel has since come and gone). For example, mainstream motherboards support dual channel, which is why memory modules are generally installed in pairs. While data are being read or written to one memory module, the second module is being prepared for reading or writing. High-end motherboards support quad channel. See SGRAM.


  Following are the most popular memory
  module speeds for each SDRAM generation.

       Memory Speed   DIMM   Voltage          (MHz)      Module  Required

  DDR4     2400     284-pin   1.2
  DDR4     2133     284-pin   1.2

  DDR3     1866     240-pin   1.35/1.5
  DDR3     1600     240-pin   1.35/1.5
  DDR3     1333     240-pin   1.35/1.5

  DDR2      800     240-pin   1.8/2.5

  DDR       400     184-pin   2.5

  SDRAM     133     168-pin   3.3
  SDRAM     100     168-pin   3.3

Matched Slots for Dual Channel
This motherboard uses colored sockets so that module pairs are inserted properly. It supports three pairs (one orange and two lavender). (Image courtesy of Giga-byte Technology Company Ltd.,

A Little Nostalgia
These 12 bits of magnetic core memory from the Whirlwind computer of the early 1950s take up about a quarter of a square inch. Today, that much space holds hundreds of millions of bits. (Image courtesy of The MITRE Corporation Archives.)
References in periodicals archive ?
With support for up to DDR400 at the memory interface and the ability to queue multiple commands at the controller, the Posedge Flash controllers offer high throughput, low host processor overhead and easy integration in any SoC development.
It supports up to 1 GB DDR400 memory in a single SODIMM socket, or it can optionally be equipped with 128 MB or 256 MB DDR400 memory soldered on the module.
Swissbit said its DDR400 2GB ECC has been tested and approved on Opteron processors by Tyan, meets the demands of servers and workstations and supports the chip kill function.
It supports up to 4GB of DDR400 memory and the tower can house four Serial ATA or SCSI hard drives with RAID 0, 1 (mirroring), or 5 (data/parity striping) data protection through an optional RAID disk controller.
com/312ee-452 * An Unofficial Guide to DDR400 or PC3200 DDR SDRAM www.
a validation and testing service company and Silicon Integrated Systems Corporation(R) (SiS), a leading core logic chipset supplier, has launched its system level validation program using the SiS648FX chipset and DDR400 memory modules.
In Conjunction With Advanced Validation Labs, SiS Launches System Validation Program for DDR400 Memory Modules
Principales caracteristicas Chipset ULi M1695/ ULI M1567; soporta tecnologias HyperTransport y Cool'n'Quiet; cuatro ranuras DIMM DDR400, hasta 4GB en RAM, una ranura AGP 8x/4x; una ranura PCI-Ex16, ranura PCI-Ex1, tres ranuras PCI, audio integrado de 7.
2 GHz processor, 17" widescreen and ATI Mobility Radeon M11 graphics, 1GB DDR400 memory, as well as full size keyboard with separate numeric keypad.
The new release is an upgrade from the company's P2PE/800 motherboard and includes 845PE and ICH4 chipsets together with high-speed DDR400 DRAM, a memory bandwidth of up to 3.
Early this year, Samsung was first to deliver engineering samples of DDR400 to major PC chipset companies, including NVIDIA, SiS and VIA.
The Emerald cluster has 1,152 GB RAM, and includes Cyclades TS3000 Console Server; a Force10 Networks E300 Series Switch; Iwill DK8-HTX motherboards; Panasas ActiveScale Storage Cluster; Pathscale InfiniPath HTX InfiniBand Adapters; Rackable Systems servers leveraging DC Power technology; Samsung Electronics 2GB DDR400 memory modules based on single-rank 1Gbit technology; and a Silverstorm 9120 InfiniBand Switch.