DDR2
From TPU Reference
DDR2 stands for Double Data Rate 2 and specifies a certain type of memory. The 2 implies that it is an increment in the development of RAM over DDR, the aging standard which it is replacing.
Technology
DDR2 has many similarities to DDR, but technological improvements allow it to clock much higher, allowing greater bandwidth
Because the bandwidth is doubled, while still running at the same clock this often creates confusion with more novice users.
With data being transferred 8 bytes at a time, DDR RAM gives a transfer rate of (memory bus clock rate) × 2 (for dual rate) × 8 (number of bytes transferred). For example a 200 MHz DDR SDRAM module has an effective bandwidth of 3,200 MB/s (200 × 2 × 8), often called DDR-400 or PC-3200.
The theoretical memory bandwidth can be further doubled by running in Dual Channel mode.
Compared to DDR1, the timings are relaxed quite a bit. A very fast setting for DDR1 is 2-2-2-4, while a fast setting for DDR2 is 3-3-3-8. Typical DDR2 memory timings are CL4 or CL5. However, in absolute terms (such as nanoseconds), the latencies work out to be about the same amount of time or even, indeed, less time on DDR2 than DDR1.
However, faster ram has become more common place in Graphics Processing Units (GPUs) DDR3 is now considered standard on a mid to high-end card, and DDR4 is becoming popular on High end cards, due to very high clocks being achieved.
Sticks/Modules
| Real clock | Rated speed | Effective Bandwidth | PC-xxxx |
|---|---|---|---|
| 200 MHz | DDR2-400 | 3,200 MB/s | PC2-3200 |
| 266 MHz | DDR2-533 | 4,267 MB/s | PC2-4200 |
| 333 MHz | DDR2-667 | 5,333 MB/s | PC2-5300 |
| 400 MHz | DDR2-800 | 6,400 MB/s | PC2-6400 |
| 500 MHz | DDR2-1000 | 8,000 MB/s | PC2-8000 |
Some manufacturers label sticks as PC2-5400 instead of PC2-5300, but both sticks run at the same speed. There are also many other unofficial ratings that manufacturers label their sticks with, such as PC2-8888.
