random access memory/types

Terms

• SDRAM = "Synchronous Dynamic Random Access Memory", meaning that they use a clock signal to synchronize things
• DDR = "Double Data Rate", meaning that they transfer two data chunks per clock cycle

Technologies

Technology	Typical Voltage	Typical Latency	Other Common Latencies Available	Data Path
DDR	2.5 V	3	2, 2.5	2 bits
DDR2	1.8 V	5	3, 4	4 bits
DDR3	1.5 V	7	6, 8, 9	8 bits
DDR4	1.2 V

Speed

Chip Tech/Speed	Real Clock	MTRR	Module Tech/Speed
DDR-200	100 MHz	1,600 MB/s	PC-1600
DDR-266	133 MHz	2,133 MB/s	PC-2100
DDR-333	166 MHz	2,666 MB/s	PC-2700
DDR-400	200 MHz	3,200 MB/s	PC-3200
DDR2-400	200 MHz	3,200 MB/s	PC2-3200
DDR2-533	266 MHz	4,266 MB/s	PC2-4200
DDR2-667	333 MHz	5,333 MB/s	PC2-5300
DDR2-800	400 MHz	6,400 MB/s	PC2-6400
DDR2-1066	533 MHz	8,533 MB/s	PC2-8500
DDR3-800	400 MHz	6,400 MB/s	PC3-6400
DDR3-1066	533 MHz	8,500 MB/s	PC3-8500
DDR3-1333	666 MHz	10,666 MB/s	PC3-10600
DDR3-1600	800 MHz	12,800 MB/s	PC3-12800

For DDR RAM, the real clock rate is always half the rated transfer speed. The module speed is in bytes/second.

Sources

• 2009-08-07 Everything You Need To Know About DDR, DDR2 and DDR3 Memories