DDR Or DDR1, DDR2, DDR3 and DDR4 are the updation of SDRAM , SDRAM stands for Synchronous Dynamic Random Access Memory these are also known as next generation of SDRAM . In these ram more improvement has made by manufacturers and performance speeds increased by using clock signal to synchronize things. DDR stands for Double Data Rate. Memories from this category transfer two data chunks per clock cycle. Translation: They achieve double the performance of memories without this feature running at the same clock rate.

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 DDR OR DDR 1 SDRAM

The DDR is known as the next generation of SDRAM, DDR RAM have greater bandwidth than the preceding single data rate SDRAM by transferring data on the rising and falling edges of the clock signal. DDR1 stands for the Double Data Rate RAM of first generation with the improvement from the SDRAM technology. The processing enhancements made by using double transition clocking, strobe based data bus, and Stub-Series Terminated Logic_2 (SSTL_2) low-voltage signaling, etc.Effectively, it doubles the transfer rate without increasing the frequency of the clock.The prefetch buffer is 2bit, which is the double of  SDRAM. The transfer rate of DDR is between 266~400 MT/s. DDR266 and DDR400 are othis type.

DDR 2 SDRAM

DDR2 stands for Double Data Rate of second generation and more enhanced to DDR1. It data processing rate is upto 6.4 GB/s. It is power consumption is lower than the DDR1.Its processing speed gained by improvement in bus signal.The prefetch buffer of DDR2 is 4 bit which is double than DDR SDRAM. DDR2 memory is at the same internal clock speed (133~200MHz) as DDR,  but the transfer rate of DDR2 can reach 533~800 MT/s with the improved I/O bus signal. DDR2 533 and DDR2 800 memory types are on the market.

DDR 3 SDRAM

 DDR3 stands for Double Data Rate of third generation of DDR SDRAM .DDR 3 SDRAM made by making more improvment on DDR 2. It has specifically improved in bandwidth and power consumption. Clock Rates on DDR 3 is from 400 MHz to 1066 MHz with theoretical peak bandwidths ranging from 6.40 GB/s to 17 GB/s. The DDR3 standard allows chip capacities of 512 megabits to 16 gigabits.DDR3 memory reduces 40% power consumption compared to current DDR2 modules . It operates on lower operating currents and voltages 1.5 V, compared to DDR2's 1.8 V or DDR's 2.5 V. The transfer rate of DDR3 is 800~1600 MT/s. DDR3's prefetch buffer width is 8 bit, whereas DDR2's is 4 bit, and DDR's is 2 bit. 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.

DDR 4 SDRAM

DDR4 SDRAM stands for Double Data Rate SDRAM of fourth generation . It operates at lower operating voltage of 1.2V and have higher transfer rate. The transfer rate of DDR4 is 2133~3200 MT/s. DDR4 adds four new Bank Groups technology. Each bank group has the feature of singlehanded operation. DDR4 can process 4 data within a clock cycle, so DDR4's efficiency is better than DDR3 obviously. 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.

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