DDR(Double Data Rate)

DDR=Double Data Rate synchronous dynamic random access memory double rate. Say strictly DDR SDRAM, people should call DDR habit, among which, called DDR SDRAM Synchronous Dynamic is the abbreviation of ideally, namely, the paper takes Access with Synchronous Dynamic Random Access Memory. And DDR SDRAM Data Rate is Double SDRAM, is the abbreviation of synchronous dynamic random access memory Double the Rate of meaning. DDR SDRAM memory in memory is based on SDRAM, still continue production system, so as to memory manufacturers to make ordinary SDRAM, only the equipment improvement, slightly of memory DDR can be realized, can effectively reduce production cost.

introduction
Working principle
In one clock cycle SDRAM only once, it is data transmission in clock for data transmission shields; And DDR memory is a clock cycle, it twice times data transmission to the stage and decline in clock each transmission time period of data, so called synchronous dynamic random access memory double rate. DDR SDRAM memory can be in the same bus with to achieve higher frequency data transfer rate.
Performance characteristics
Compared with using DDR SDRAM, more advanced synchronous circuit, make the nominated address, data transmission and output main steps, and keep both independently execute completely in sync with the CPU; DDR tow vehicle using DLL Locked Loop, Delay (lock Loop provides a data filtering signal) technology, when data effectively, storage controller can use this data filtering signal to accurate location data, every 16 times, and once again the output from different memory module of synchronous data. DDR essentially needs to improve the clock frequency can double the speed of increase SDRAM, and it allows the rise in clock pulse along and down along the readout, hence its speed is twice the standard SDRAM.
From the appearance on compared with DDR SDRAM volume, and they have differences are not the same size and the same sutural distance. But for DDR SDRAM more than 184 sutural, a 16 pins, mainly contains a new control, clock, power and grounded signal. DDR memory USES is the support of voltage 2.5 V SSTL2 standard, not SDRAM use of 3.3 V LVTTL standard voltage.
DDR memory frequency
DDR memory frequency can work with frequency and equivalent frequency, said two ways of working frequency is the memory particles practical work frequency, but because the DDR memory can in pulse the rise and fall of the transmission of the data, so along all the data transfer equivalent frequency is twice the working frequency.
What is DDR1
Sometimes people will old storage technology, which is called DDR DDR1 with DDR2 distinguished. Despite the general is to use "DDR", but with the same meaning DDR DDR1.
DDR1 specifications
DDR SDRAM 200: DDR memory chips - in 100 MHz run DDR SDRAM - 266: DDR memory chips in - under 133 MHz running DDR SDRAM quarterly: DDR memory chips in 166 - run - 400 MHz DDR SDRAM memory chips, DDR - in 200 MHz formulated under the DDR JEDEC running (supreme specifications) DDR SDRAM - 500: DDR memory chips - run in 250 JEDEC MHz (not for DDR specifications) DDR SDRAM - 600: DDR memory chips - at 300 MHz JEDEC run under the DDR (not formulated specification) DDR SDRAM 7: DDR memory chips - run at 350 JEDEC MHz (not for DDR specifications)