Stick with it

Almost all the new core-logic PC motherboards on the market now support new DDR3 memory, and DDR3 modules are now beginning to appear in stores too. Windows explains how these DDR3 sticks work and what benefits they can bring to your next rig.

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By  Jason Saundalkar Published  January 5, 2008

Double Data Rate (DDR) RAM (Random Access Memory) has been around for over five years, and in that time the technology has been revised a number of times.

Each revision brings with it a number of improvements compared to its predecessor. Generally the most notable are higher transfer rates and lower power requirements. The latest version, DDR3, continues this trend, making it faster at moving data and more power-friendly than DDR2, its immediate predecessor.

DDR memory, also known as DDR SDRAM (Synchronous Dynamic Random Access Memory), is different from standard SDRAM memory because it runs at double the rate. It does this by transferring data on the rising and falling edges of the clock signal as opposed to just on the rising edge, as was the case with standard RAM.

This doubles the data transfer rate without actually increasing the frequency of the memory bus (a bus being the an electrical conductor that makes connects several circuits.) So whilst regular memory running at 100MHz is actually running at 100MHz, a 100MHz DDR module is actually transferring data as if it's running at 200MHz.

When DDR memory technology was initially launched, its main competitor on the market came was RDRAM (Rambus Dynamic Random Access Memory). In contrast to DDR RAM, RDRAM modules ran with extremely high latencies, produced far more heat, were complex to produce and were very expensive. As a result, most memory manufacturers gradually dropped support for RDRAM from their chipsets, adopting DDR memory and its future variants instead.

DDR3 delights

DDR3 RAM offers a number of key advantages. Firstly, it has the ability to run the I/O (Input/Output) bus at four times its normal speed, which ultimately results in faster data bus transfer speeds. This effectively translates into higher peak throughputs, so whereas the fastest DDR2 memory modules can manage a peak throughput of 8533Mbytes/sec, the fastest current DDR3 modules are capable of delivering rates of 12,800Mbytes/sec.

This rate is expected to peak even higher when faster DDR3 modules are released on the market. (Vendors such as OCZ and Corsair are already shipping 1800MHz modules though their wide-scale availability will likely kick in during the second quarter of this year.)

Another big advantage DDR3 offers when compared to DDR2 comes in the form of its lower power requirements. While 800MHz DDR2 memory modules generally need 1.8 volts (higher frequency modules require even more), even the fastest official DDR3 module today (1600MHz) requires only 1.5 volts. This is a big advantage for notebook users in particular, as lower power consumption translates into a longer battery life. In terms of desktop PCs, lower power consumption means you'll save cash on your electricity bills. The low power draw also translates into cooler operating temperatures, potentially making DDR3 modules better suited to overclocking.

The DDR3 standard is also designed to allow for memory chip capacities of 512-mebibits (mega binary binary digit - 1 mebibit = 1,048,576 bits or 1Mbyte) to eight-gibibits (giga binary binary digit - 1 gibibit = 1,073,741,824 bits or 128Mbytes). This effectively means that you can have single DDR3 module with up to 2Gbytes of capacity, thus allowing motherboards with four DIMM sockets to handle a maximum of 8Gbytes of memory.

Setting standards

The Joint Electron Device Engineering Council or ‘JEDEC' is an international body of semiconductor manufacturers. This group sets integrated circuit standards such as speed, voltages. timings and more. JEDEC was formed to standardise the operating specifications of a particular technology, in this case DDR3, when it's released.

Manufacturers generally use these specs (see the table on the right) to build memory, and this ensures modules will be compatible with motherboards following the specification. Most firms involved in producing enthusiast or overclocking-aimed modules however, such as Corsair, OCZ and Mushkin, use these as guidelines and frequently build sticks operating slightly outside of these specifications (mostly in terms of their transfer speed and voltage). Generally, there is almost no risk involved when using memory that doesn't follow a JEDEC standard.

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