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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 ?
0+ media access controller (MAC) with channel bonding capabilities, an 800-DMIPS communications processor, a DDR266 DRAM interface, Ethernet and USB interfaces, and expansion capabilities to support VoIP and wireless connectivity.
Dataram's 8GB DRHZX2000/8192, for the zx2000 workstation, and DRHZX6000/8192, for the zx6000 workstation, contain two registered ECC DDR266 DIMMs built with advanced, high-density one-gigabit DRAMs.
58B x6) MEMORY: 256MB (128MB DDR266 x2) up to 4 GB DRIVE BAYS: 6 EXPANSION SLOTS: 4 PCI-X (64bit/100MHz x4), 2 PCI (32bit/33MHz x2) RACK SUPPORT: Micro-tower CHIPSET: INTEL E7501 High End PRICE: Unavailable PROCESSOR: Expandable Express 5800 140Rc-4 up to four Xeon Processor MP 2.
The 120Rd-1 and 120Rf-2 feature I/O capabilities, a 533MHz Front Side Bus, 12GB of DDR266 SDRAM and embedded, Ultra 320 SCSI and Gigabit Ethernet controllers, an Intel E7501 chipset and up to two Intel Xeon processors running at speeds of up to 2.
The new notebook incorporates a 15-inch XGA display and comes standard with 256MB DDR266 onboard system memory upgradeable to 512MB, a nine-cell Lithium ion battery and two Type II or one Type III PC card slots.
Customers can increase memory capacity to 128GB by installing DIMMs in all 32 available slots, however the memory will run at DDR266 speed.
Built around Infortrend's proprietary ASIC266 dual PCI-X architecture, the ES A24F-R2224 features redundant RAID controllers, eight FC-2G host ports, DDR266 cache memory, two dual-fan cooling modules, N+1 redundant power supplies, and an optional battery backup unit.
The 845PE chipset offers DDR333 memory and AGP4x support and the Intel 845GV features DDR266 main memory capability and a 533MHz or 400MHz system bus.
Built around Infortrend's proprietary ASIC266 dual PCI-X architecture, the subsystem features dual-redundant RAID controllers for the highest levels of redundancy and performance, dual 4Gb Fibre Channels per controller, dedicated point-to-point drive channels, DDR266 cache memory, two dual-fan cooling modules, redundant power supplies, and an optional hot-swappable battery backup unit.
Dataram's 512MB and 1GB upgrade (DRL650/512 and DRL650/1024 respectively) consists of a single ECC DDR266 DIMM that is 100% compatible with the Dell Precision 450 and 650 workstations and is backed by Dataram's lifetime warranty and free technical support.
Built around Infortrend's proprietary ASIC266 dual PCI-X architecture, the subsystem features a single RAID controller, two SCSI host channels, DDR266 cache memory, two dual-fan cooling modules, three power supplies, and an optional battery backup unit.
As the newest addition to Samsung's DDR SDRAM portfolio, the 400Mbps (200MHz) DDR devices are ideal for use as PC system main memory, offering three times the performance of Single-Data-Rate PC 133 SDRAM and 50 percent more bandwidth than mainstream DDR266.