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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 ?
The 13.3" 2.16GHz white MacBook features a 667MHz front-side bus, 1GB of 667MHz DDR2 SDRAM, 120GB SATA hard drive at 5400rpm, DVD+R DL/DVDRW/CD-RW optical drive, Intel Graphics Media Accelerator 950 and Gigabit Ethernet port, with a USD1,299 suggested retail price.
The eMachines T5088 Desktop PC Configuration includes Intel Pentium 4 Processor 641 (3.20GHz, 2MB L2 cache, 800MHz FSB), 512MB DDR2 memory expandable to 2GB and 160GB 7200RPM hard drive, priced from USD399.99 after rebate.
TELECOMWORLDWIRE-22 May 2007-Ultra low latency DDR2 800MHz HyperX memory modules announced by Kingston Technology(C)1994-2007 M2 COMMUNICATIONS LTD
(NYSE:MU), delivered the industry's first four gigabyte (4GB) DDR2 registered dual in-line memory module (RDIMM) to Intel Corporation.
Samsung Electronics Co., Ltd., a leader in advanced semiconductor memory technology, announced recently that its advanced DDR2 memory solutions are ready to meet the needs of a new generation of high performance PCs and servers.
Worldwide Computer Products News-11 January 2007-Kingston Technology introduces 1.2 GHz DDR2 HyperX memory modules(C)1995-2007 M2 COMMUNICATIONS LTD
Elpida Memory, Inc (Elpida) has announced volume production of its 512 Megabit-based 2 Gigabyte DDR2 registered dual in-line memory modules (DIMMs).