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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 ?
I'M Intelligent Memory's high capacity DDR2 SDRAM IC's.
Longmore emphasizes that DDR2 does not initiate the high levels of SNAIL1.
With its low power and performance for multi-tasking, rich media and the Internet, the features and benefits of 'Oak Trail,' in combination with Micron's 2Gb 50nm DDR2 provide a powerful solution for our joint customers' design needs.
ZOTAC makes a product for all markets and segments, with the addition of the new GeForce 9400GT Synergy Edition and GeForce 9400GT DDR2 1GB, we now have a low-profile graphics card for small form factor users that want to upgrade to the latest GeForce 9 graphics architecture and a entry-level graphics card with 1GB of video memory" said Carsten Berger, marketing director, ZOTAC International.
For more detailed information on ValueRAM DDR2 technology and Kingston memory products, visit the Kingston Technology Web site at http://www.
The DDR2 SDRAM memory generator is a TCL/TK-based tool that supports leading memory vendors and preserves a large library of part numbers for each supported memory vendor.
Elpida 512 Megabyte DDR2 SO-DIMMs are currently available in samples.
Kingston has been working diligently on the DDR2 solution for quite some time and we are pleased to support the system builder and the enthusiast market with such a high-speed product," added Wu.
5-volt DDR2 Aspen Memory modules are currently designed into production data center server systems.
the world's leading supplier of programmable solutions, today announced support for a 400 Mbps DDR2 SDRAM interface (DDR2-400) with its proven low-cost 90 nm Spartan(TM)-3A and Spartan(TM)-3AN FPGAs.
Worldwide Computer Products News-18 April 2006-Kingston Technology introduces Low Latency DDR2 memory modules and expands Ultra Low Latency(C)1995-2006 M2 COMMUNICATIONS LTD http://www.
Elpida), Japan's leading supplier of Dynamic Random Access Memory (DRAM), today announced the availability of 4 Gigabyte DDR2 Registered Dual In-Line Memory Modules (DIMMs) that offer high-density and high-performance benefits for server applications.