DDR RAM Generational Increases
-
Hello everyone,
I've been trying to find this answer for days with no luck so I finally decided to turn to the forums to see if I can solve this once & for all!
I know that each generation of DDR RAM sees a 2x increase in the data rate (MT/s), but I am unsure of why this happens. From what I've read, most sources attribute it to the doubling of the data bus frequency, but what bugs me is that the prefetch amount also doubles each generation (except for maybe DDR3-DDR4) & I am unclear what role this plays in it. What do the prefetch units of 2n, 4n, 8n, etc... mean exactly & what role do they play in the generational doubling of DDR?
Thanks in advance!
-
@John-Long,
The number to watch is not on the result (MT/s) but on what makes it happen is that prefetch number. This is the number that continues to double between the generations that you mentioned. That number is about how much data can be accessible at any one point in time. This time that number is about bits, and bits doubling allowing more binary data in in each generation. the 2n is 2^2 = 4 bits = 4 , etc. by the DDR5 it's 2^16 = 16 bits = 65, 535. Each successive generation has been able to process more data at the faster speeds you've mentioned. An analogy: how many people you can carry, on a speed-bike you can carry 1 or 2 people really fast, but it's still 1 or 2 people. But if I drive a school bus that has more seats but also is faster than the speed bike...how many more people get to the destination faster? Those bits then are about capacity at a given speed.This is the tricky part. If you have a mobo that you can mix and match ram, which most don't but if you do...it will only go as fast as the slowest speed ram you have...which means you can make faster RAM go slower; but you cannot make slower RAM faster.
