How is RAM clock speed actually calculated?

cooksta · Mar 29, 2013

Ok so after doing a bit of reasearch, I've found a ton of information about RAM.

I've actually got a fairly decent understanding of smaller details of how memory is accessed, CAS latencies, even CPU/Memory bandwidth issues.

I'm still at a complete loss at how RAM clock rate is determined (MHz).

From my understanding, CPU clock rate is calculated by taking the FSB (or BCLK) speed and multiplying it by the CPU multiplier rate.

So with a FSB of say 133MHz, and a multiplier of 20, we arrive at a total of 2660 MHz clock rate.

Is this how RAM clock speed is calculated? I know RAM is intricately tied to the bus rate, I just can't seem to figure out how exactly.

Is there some big obvious point that I'm missing?

Dopamin3 · Mar 29, 2013

DDR stands for double data rate. Memory frequency is derived from your BCLK/FSB (Intel) or HT (AMD) multiplied by a memory multiplier. Example on 1155 most people keep BCLK around 100. 100 * 8 memory multiplier = 800mhz and since it's DDR, the memory is running effectively at 1600mhz. AMD the HT starts at 200, so keeping it at 200 with a memory multiplier of 3.33 = 666mhz so DDR effective rate is 1333mhz.

Keep in mind on older CPUs for Intel the FSB is quad pumped. So when they advertise let's say a 1333mhz FSB, it's actually 266mhz and DRAM frequency is derived from that. So basically, just like CPU frequency is determined by the reference clock * a multiplier, memory is determined reference clock (BCLK/FSB/HT) * a multiplier. Some people refer to these as dividers but it's all just multiplication.

cooksta · Mar 29, 2013

Ok, that has cleared up things in a massive way, thanks a ton mate.

How is RAM clock speed actually calculated?

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