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McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


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(Synchronous DRAM) The type of dynamic RAM memory chip in wide use since the mid-1990s. SDRAM divides the chip into two cell blocks and interleaves 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) Since 2000
DDR SDRAM doubled the data transfer rate by using both the rising and falling edges of the clock cycle, and more speed is achieved with each generation (see below).

Memory Channels
Motherboards may support one, two or four channels. More than one channel requires installing modules in a prescribed order (see image below). See GDDR.

        Clock    Transfer        DIMM        Speed      Rate         Module DDR    (MHz)     (MT/s)    (V)  Pins

 DDR5 1600-3200  3200-6400  1.1  288
 DDR4  800-1600  1600-3200  1.2  284
 DDR3  400-1200   800-2400  1.5  240
 DDR2  200-533    533-800   1.8  240
 DDR   100-200    200-400   2.5  184
 SDRAM  66-133     66-133   3.3  168

Matched Slots for Dual Channel
Dual-channel motherboards use color-coded sockets so that DDR memory modules are inserted in pairs. This motherboard supports two pairs of DIMM modules (see memory module).

DDR RAM Modules Are "Keyed"
This example shows the notching of three DDR generations. Modules and slots are "keyed" to prevent the wrong DDR version from being inserted. See memory module.

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 billions of bits. (Image courtesy of The MITRE Corporation Archives.)
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References in periodicals archive ?
Fremont, CA, February 18, 2011 --( Newest Intro Designed for Rugged Environments; Includes Large 15.6" Display with HD Resolution, Intel[R] Compliant HD Stereo Audio, and Two Dual Channel DDR III Memory Slots
In addition, the VGA port supports two PCI Express x 16 Video Cards, and has a memory capacity up to 4 GB of 266/333/400 MHZ Dual Channel DDR SDRAM.
"Extensive hardware and software testing, along with proven technology including a compelling dual channel DDR memory interface and dual VGA-monitor capability, ensures IT buyers and business users of a compatible and reliable platform."
The first release is the IntelliStation M Pro 6219 which features a choice of graphics accelerator, up to 4.0GB dual channel DDR memory, front-mounted USB 2.0 ports, an Intel Pentium 4 processor up to 3.06GHz, 533MHz system bus, 8X AGP graphics, Ultra320 SCSI and integrated Gigabit Ethernet.
The ePCI-201 includes a set of standard features including the latest generation Intel[R] Pentium[R]4 processor up to 3.4 GHz, up to 800 MHz front side bus, dual channel DDR memory, two-channel serial ATA, on-board ATI[R] Mobility[TM] Radeon[TM] M7 or M9 video controller, dual Gigabit Ethernet and 64-bit at 66 MHz bus support.