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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 ?
The IOS-7200 Industrial PC is equipped with an embedded AMD Geode LX800 500MHz CPU with 512MB of DDR400 DRAM that runs on Windows Embedded Standard or Linux.
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.
With Intel's memory optimising Performance Acceleration Technology (PAT), Serial ATA with RAID and performance-enhanced ECC dual-channel DDR400 memory, Shuttle's latest XPC, offers unmatched performance and stability.
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.
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
The new DDR400 Ultra Low Latency HyperX with its 2-2-2 timings make it the ideal module for gamers wanting high density, low latency configurations in today's AMD(R) based desktop systems," said Mark Tekunoff, senior technology business manager, Kingston.
2 GHz processor, 17" widescreen and ATI Mobility Radeon M11 graphics, 1GB DDR400 memory, as well as full size keyboard with separate numeric keypad.
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.
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.
Known as the World's Most Efficient Server, a typical configuration deployed in an AC data center draws a peak of less than 150 watts in a design featuring two dual-core processors (four total cores), 4 GB DDR400 RAM and one Terabyte of SATA storage -- with a mere 500 BTU/hour of peak thermal output.