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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 ?
This was the genesis of the current DDR SDRAM device design and manufacturing efforts.
Nevertheless, and in spite of the unknowns, a general overview and explanation of where SDRAM and other future technologies may head will serve to give us a better grasp of key issues.
Via is working on a chipset that will support PC-133 SDRAM memory, which it and others have positioned as an "evolutionary alternative" to Intel's proposed support for Direct Rambus memory.
It supports up to 512MB of SDRAM, with dual USB connectors and four PCI slots.
Other features include two serial ports, four USB ports, a PCI Bus Master 10/100Base-TX Ethernet controller and support for up to 512MB DDR SDRAM.
The model comes equipped with a 20-GB 7200 rpm Quiet Seek and Idle SMART IIII Ultra ATA/100 hard drive, 128-MB SDRAM, a CD-ROM Drive and a removable 1.44-MB diskette drive.
Worldwide Computer Products News-22 May 2002-Micron reveals samples of new 256MB SDRAM (C)1995-2002 M2 COMMUNICATIONS LTD
Those include finalizing the introduction of PC133MHz SDRAM parts, seen as a stepping stone for DDR 266MHz technology.
The miniature MCP consists of a combination of memory chips, such as SRAM, SDRAM, NOR Flash memory and NAND Flash memory, and has a total capacity of 776 megabits (Mb) in one sample application.