DDR-II

From IeXwiki

DDR-II SDRAM (Double Data Rate Two Synchronous Dynamic Random Access Memory) is a [omputer memory technology that, as of 2005, is becoming the mainstream standard for personal computer memory. DDR-II is part of the SDRAM family of random access memory technologies.

The advantage of DDR-II over DDR-I is its ability to work at higher effective clock speeds.

DDR-II represents a further doubling of the "effective" clock rate over DDR, which itself doubled the effective clock rate of SDR. With a clock frequency of 100 MHz, SDR will transfer data on every rising edge of the clock, thus achieving an effective 100 MHz transfer rate. Like DDR, DDR-II will transfer data on every rising and falling edge of the clock (double pumped), achieving an effective rate of 200 MHz. Other speed increases are achieved through an increased number of buffers, an improved prefetch, reduced electrical requirements, improved packaging and on-die termination. However, latency is increased.

Power savings are achieved primarily due to the improved process technology used to manufacture chips, but also the lower clock frequency used. A DDR-II product can use a clock frequency of 1/4 that of SDR, whilst maintaining the same bandwidth. A lower clock frequency is both easier to route across a circuit board, and results in lower power usage, particularly when the data bus is latent.

[edit]

Chip specification

  • PC2 3200 (DDRII-400): memory specified to run with 400 MHz (bandwith 3.2 MB/s)
  • PC2 4200 (DDRII-533): memory specified to run with 533 MHz (bandwith 4.2 MB/s)

The following new DDRII-SDRAM specifications are currently rare and highly expensive and is only used for top end Intel 925X or above chipset models.

  • DDRII-600
  • DDRII-733
  • DDRII-800
  • DDRII-933
  • DDRII-1066

DDRII-SDRAM are made with the following memory amount:

  • 64 MB (rare and obsolete)
  • 128 MB (becoming rare)
  • 256 MB (lower mainstream)
  • 512 MB (upper mainstream)
  • 1024 MB (top end and expensive)
[edit]

History

The first commercial product to use the technology was the nVidia GeForce FX 5800 series of graphics cards. The 5900 series reverted to DDR, as did the 5950, but nVidia's old mainstream card, the 5700 Ultra, used DDR-II clocked at 900 MHz (compared to 800 MHz on the 5800, and 1GHz on the 5800 Ultra). ATI Technologies's Radeon 9800 Pro with 256 MB memory (not the 128 MB version) also used DDR-II, but this was because DDR-II requires fewer pins than DDR. The Radeon 9800 Pro 256 MB only runs its memory at 20 MHz faster than the 128 MB version, primarily to counter the performance loss caused by higher latency and the increased number of chips. It's thought that the DDR-II used on the 9800 Pro 256 MB is actually memory that was supposed to be used on the GeForce FX 5800 series, but ended up being unused after nVidia decided to halt production of the 5800 line. The newest ATI chip, the 9800XT reverted to DDR, and ATI later began to use GDDR-3 memory on their Radeon X800 line.

It's important to note that the DDR-II memory used on graphics cards (sometimes referred to as GDDR-2) is actually something of a melding of DDR and DDR-II technologies, and had trouble with heat overproduction owing to the fact that DDR voltages were still being used. ATI has since created GDDR-II memory, which is more true to the DDR-II specifications (though has a few additional features that help suit it to graphics cards), and has largely replaced DDR-II in graphics cards.

Retrieved from "http://www.iexbeta.com/wiki/index.php/DDR-II"