What's the real difference between RAM sticks with equivocal speeds?

[DragonGunner]

I've had it explained to me that CAS latency and frequency of RAM units are fairly useless numbers on their own. The frequency dictates how many ticks per second the chip can pump out, while the CL dictates the number of ticks the chip requires to read/write/whatever data. What I was told to do, was to divide the frequency by the CL, which returns the number of actual changes in data that the stick can do each second - the higher that number, the faster the RAM.

Not too complicated.

What I don't understand is why companies differentiate so finely between different speeds. For instance, I found three DDR4 8GB, dual channel, non-ECC sticks; the first at 3200Mhz CL16, the second at 3000Mhz CL15, the third at 2800Mhz CL14 - all manufactured by the same company, each one a few bucks pricier than the next.

So my question is, what is the difference (if it exists) between equivalent frequency/CL ratios? Would there be any particular gain or detriment to buying sticks with lower CL/higher freq?

 

[greens]

Sure, to give you a general idea of what you're looking at:
true latency (ns) = clock cycle time (ns) x number of clock cycles (CL)

So we can find that
True Latency = CAS * 1000 / Speed

So we can see that
4.375=14*1000 / 3200
Modern DDR4 ram with low CAS and high clock is very, very fast.

8.57=16*1000 / 1866
Older DDR3 ram with decent CAS and ok clock, is nothing compared to the new stuff.

Would you be able to perceive a difference between 8ns and 4ns? Probably not... but it is much, much faster.

You can use this math to compare very similar RAMs to see if you're better off with a lower CAS or a higher frequency, etc.