What is DDR4

DDR is also known as double-rate SDRAM Dual Date Rate SDRSM. DDR SDRAM is a high-speed CMOS memory with dynamic random access. The Solid State Technology Association of JEDEC in the United States published the Double Data Rate Synchronous Dynamic Memory (DDR SDRAM) specification JESD79 in June 2000. Data transmission can be performed on the upper and lower edges of the clock trigger edge, so the bandwidth can reach 2.128GB/s even at a bus frequency of 133MHz. DDR does not support 3.3V LVTTL but supports 2.5V SSTL2 standard. It can still be used today. The manufacturing cost of a production system with SDRAM is slightly higher than that of SDRAM but far less than the price of Rambus. DDR memory represents a direction of memory development that can compete with Rambu in the future.

DDR2 (Double Data Rate 2) SDRAM is a new generation memory technology standard developed by JEDEC (Joint Electronic Equipment Engineering Committee). The biggest difference between it and the previous generation DDR memory technology standard is that although the same uses the rising clock/ The basic method of data transmission while falling delay, but DDR2 memory has twice the pre-read capacity of the previous generation DDR memory (ie: 4bit data read pre-fetch). In other words, DDR2 memory can read/write data at 4 times the speed of the external bus per clock, and can run at 4 times the speed of the internal control bus.

1. Fundamental:

The 400 in DDR400 refers to the memory bandwidth, which is a converted value of the operating frequency. DDR400 memory runs at a clock frequency of 200MHz, and DDR can access data twice per clock cycle, so it is equivalent to running at 400MHz (200MHz×2). The same algorithm, DDR2 533 memory, running at 133MHz, can access data four times per clock cycle, which is equivalent to 533MHz (133MHz×4).

Of course, the larger the value and the higher the frequency, the faster the memory speed will definitely be. The frequency of DDR400 memory is close to the limit. Obviously DDR2 runs at a much lower frequency than DDR memory, but it can provide better performance, so it will be the mainstream in the next two years.

DDR3, 4 memory is already available, which is twice as fast as DDR2. Currently, it is mainly used for graphics cards with higher speed requirements for video memory. It will definitely be gradually used for main memory in the future.

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