What does a DDR mean?

Ddr=double Data Rate Double rate synchronous dynamic random memory. Strictly speaking, DDR should be called DDR SDRAM, which is known as the DDR, where SDRAM is the abbreviation of synchronous dynamic Random access memory, i.e. synchronous dynamically random access memory. The DDR SDRAM is the abbreviation of double Data Rate SDRAM, which is the meaning of double speed synchronous dynamic random memory. DDR memory is developed on the basis of SDRAM memory, still follow the SDRAM production system, so for the memory vendors, only a little improvement of the equipment to create common SDRAM, can achieve the production of DDR memory, can effectively reduce costs.

Working principle

SDRAM transmits only once data in a clock cycle, it is in the clock rising time to carry on the data transmission, but the DDR memory is a clock cycle transmits two times the data, it can transmit the data each time in the clock rise time and the descent period, therefore is called the double rate synchronous dynamic random memory. DDR memory can achieve higher data transfer rates at the same bus frequency as SDRAM.

Performance features

Compared to SDRAM: DDR uses a more advanced synchronization circuit, so that the specified address, data transmission and output of the main steps are performed independently, but also to maintain full synchronization with the CPU; DDR used DLLs (Delay Locked Loop, delay-locked loop to provide a data filter signal) technology, When the data is valid, the storage controller can use this data filtering signal to pinpoint data, output once every 16 times, and resynchronize data from different memory modules. DDR essentially does not need to raise the clock frequency to increase the SDRAM speed, it allows the clock pulse to rise along and down along the reading data, so its speed is twice times the standard SDRAM.

DDR differs from SDRAM in terms of shape volume, and they have the same size and the same pin distance. But the DDR is 184 pins, 16 more pins than SDRAM, including new controls, clocks, power supplies and grounding signals. DDR memory uses the SSTL2 standard that supports the 2.5V voltage, rather than the 3.3V voltage LVTTL standard used by SDRAM.