DDR means Double Data Rate it can fatch data on both the up and the down cycles of the clock. DDR SDRAM, as the first generation of DDR memory, the prefetch buffer is 2bit, which is the double of SDR SDRAM. The data transfer rate of DDR is between 200~400 MT/s. DDR266 and DDR400 are of this type. It’s taken voltage 2.5 to 2.6 volt. Number of pins 188. Dimension/size: 14.2 X 0.5 X 4.3 Cm. The common sizes are 256mb, 512mb and 1Gb.
DDR2 next generation of DDR memory. It’s benefit is the ability to operate the external data bus twice as fast as DDR. It’s provides maximum data transfer rate 3,200 to 8,533 MB/s. Clock speed 400 to 1,066 MHz. It’s taken voltage only 1.8 volt. Number of Pins 240. The common sizes are 512mb, 1Gb and 2Gb. Transfer rate 4.2 to 6.4GB/s. 5-6ns latency.
DDR3 RAM replaces the 2x clock multiplier with a 4x clock multiplier, thus running at 4 times the memory transfer rate. But see here pin number is same 240 pins. DDR3 memory reduces 40% power consumption compared to current DDR2 modules, allowing for lower operating currents and voltages 1.5 V. DDR3 also adds two functions, such as ASR (Automatic Self-Refresh) and SRT (Self-Refresh Temperature). They can make the memory control the refresh rate according to the temperature variation. DDR3 was first released in 2007.
DDR4 RAM support highend motherboard only just like 6th/7th/8th Gen Core and AMD’s AM3/AM3+. Here are latency of 12.75 nanoseconds. DDR4 provides 21.3GB/s of bandwidth and lower operating voltage (1.2V) and higher transfer rate 17-21.3GB. DDR4 also adds some functions, such as DBI (Data Bus Inversion), CRC (Cyclic Redundancy Check) and CA parity. They can enhance DDR4 memory’s signal integrity, and improve the stability of data transmission/access. Bus Clock speed 1066-1600(MHz).