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SDRAM

(Synchronous DRAM) A type of dynamic RAM (DRAM) memory chip that has been widely used since the late 1990s. SDRAM chips eliminated wait states by dividing the chip into two cell blocks and...

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Dictionary

Definition: SDRAM

(Synchronous DRAM) A type of dynamic RAM (DRAM) memory chip that has been widely used since the late 1990s. SDRAM chips 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.

Double Data Rate (DDR)
DDR SDRAM doubles transfer rates by transferring data on both the rising and falling edges of the clock. DDR uses a 184-pin DIMM module in contrast to the 168-pin DIMM of earlier SDRAMs. Laptops use 200-pin SODIMM modules.

DDR2 and DDR3
DDR2 chips increase data rates using various techniques such as on-die termination, which places the terminating transistors that eliminate excess signal noise on the chip itself. DDR3 offers a moderate speed improvement over DDR2, owing to 90 nm fabrication (see feature size).

DDR2 and DDR3 use 240-pin DIMM modules. DDR, DDR2 and DDR3 modules are all keyed differently so that they cannot be inserted into the wrong motherboard slots.

Dual Channel
Chipsets on the motherboard may support two independent memory controllers, which allow access to two memory modules simultaneously (upstream data on one 64-bit channel; downstream data on the other). Channels can be configured as two 64-bit or one 128-bit. Modules must be installed in matched pairs unless the chipset has an option for mismatched modules. See memory module and SGRAM.

In the following list, the single channel speeds are given. If dual channel is implemented, the memory speed and data rates are doubled, and many memory products use the doubled rate in their chip designations.

       Single           Single
       Channel          Channel
       Memory           Data
       Speed            Rate
 Type  (MHz)  Symbol    (GB/sec)   DIMM
 DDR3   800  PC3-12800   12.8    240-pin
 DDR3   667  PC3-10600   10.6    240-pin
 DDR3   533  PC3-8500     8.5    240-pin
 DDR3   400  PC3-6400     6.4    240-pin
 DDR2   533  PC2-8500     8.5    240-pin
 DDR2   500  PC2-8000     8.0    240-pin
 DDR2   400  PC2-6400     6.4    240-pin
 DDR2   375  PC2-6000     6.0    240-pin
 DDR2   333  PC2-5300     5.3    240-pin
 DDR2   266  PC2-4200     4.2    240-pin
 DDR2   200  PC2-3200     3.2    240-pin
 DDR    266  PC-4200      4.2    184-pin
 DDR    200  PC-3200      3.2    184-pin
 DDR    166  PC-2700      2.7    184-pin
 DDR    133  PC-2100      2.1    184-pin
 DDR    100  PC-1600      1.6    184-pin
                  Single Channel
                      Speed
 SDRAM  133         1.1 GB/sec   168-pin
 SDRAM  100         800 MB/sec   168-pin

Matched Slots for Dual Channel
Motherboards that support dual channel use color coded memory slots so that module pairs are inserted properly. This example shows three pairs (one orange and two lavender). (Image courtesy of Giga-byte Technology Company Ltd., www.giga-byte.com)

SDRAM

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.)

THIS DEFINITION IS FOR PERSONAL USE ONLY
All other reproduction is strictly prohibited without permission from the publisher.
© 1981-2010 The Computer Language Company Inc. All rights reserved.

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