DDR

From TPU Reference

racdomrelt montrc4terta eldarsi DDR stands for Double Data Rate and specifies a certain type of memory.

Before DDR, data could only been transferred on one edge of the clock signal. With DDR, data is transferred on both the rising and falling edge of the clock signal.

The advantage of this approach is that you do not have to increase the number of data signal lines to the memory.

Double Data Rate is also known as double pumped, dual pumped or double transition.

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 (200 × 2 × 8 × 2 = 6400MB/s). This requires Dual Channel memory configuration.

Real clock	Rated speed	Effective Bandwidth	PC-xxxx
100 MHz	DDR-200	1,600 MB/s	PC-1600
133 MHz	DDR-266	2,100 MB/s	PC-2100
150 MHz	DDR-300	2,400 MB/s	PC-2400
166 MHz	DDR-333	2,700 MB/s	PC-2700
183 MHz	DDR-366	3,000 MB/s	PC-3000
200 MHz	DDR-400	3,200 MB/s	PC-3200
217 MHz	DDR-433	3,500 MB/s	PC-3500
233 MHz	DDR-466	3,700 MB/s	PC-3700
250 MHz	DDR-500	4,000 MB/s	PC-4000
266 MHz	DDR-533	4,200 MB/s	PC-4200
275 MHz	DDR-550	4,400 MB/s	PC-4400
283 MHz	DDR-566	4,500 MB/s	PC-4500
300 MHz	DDR-600	4,800 MB/s	PC-4800

See also

• DDR2
• DIMM
• EDO
• SDRAM