Memory bandwidth Calculation

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Memory bandwidth Calculation formula: Bandwidth = memory core frequency x memory bus digits x multiplication factor.
Let me start with the DDR technology, DDR using clock pulse rise, descent along each pass data, 1 clock signals can be transmitted twice times the SDRAM data, so also known as double rate SDRAM. Its multiplication coefficient is 2. DDR2 still uses the clock pulse to rise, drop the data to pass the technology (not 2 times), but a prefetch 4bit data, is the DDR one time to read 2bit twice times, therefore, its multiplier coefficient is 2x2=4. DDR3 as an upgraded version of DDR2, the most important change is a pre-read 8bit, is DDR2 twice times, DDR 4 times times, so, its multiplier coefficient is 2x2x2=8.

One thing to add is that memory has three different frequency metrics, which are core frequencies, clock frequencies, and effective data transmission frequencies. The core frequency is the operating frequency of the memory cell array, which is the real operating frequency of the memory, the clock frequency is the transmission frequency of I/o buffer (input/output cache), and the effective data transmission frequency is the frequency of the Memory. DDR3 memory from the storage unit to prefetch 8Bit of data, in the I/obuffer (input/output cache) in the rise and fall of the simultaneous transmission, so the effective data transmission frequency reached the storage unit core frequency of 8 times times. At the same time the clock frequency of DDR3 memory increased to 4 times times the core of the storage unit. That is to say, the core frequency of ddr3-800 memory is only 100MHz, its I/O frequency is 400MHz, and the effective data transmission frequency is 800MHz. From the sdram-ddr era, the data bus bit width clock has not changed, all 64bit, but the use of dual-channel technology, can obtain 64x2=128bit bit width.

The following calculates the bandwidth of a nominal DDR3 1066 memory strip at the default frequency:

1066 refers to the effective data transmission frequency, divided by 8 is the core frequency. One memory only uses the single channel mode, the bit width is 64bit. So the memory bandwidth = (1066/8) x64x8=68224mbit. It can be concluded that if the memory is working at nominal frequencies, it is possible to simplify the formula directly with the nominal frequency x bit width.  Again according to 8bit (bit) =1byte (byte), get 68224/8=8528MBYTE=8.328125GB. Again with two nominal 1066 overclocking to 1200 of the DDR3 memory, composed of two channels after the bandwidth: overclocking to 1200, the memory core frequency should be 1200/8=150mhz, while the dual-channel bit width =128bit: bandwidth =150x128x8=153600mbit= 18.75GB