[SOLVED] Difference Between "Memory Clock Speed" & "I/O Bus Clock Speed"

Jarrodm08

Commendable
Sep 27, 2016
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Looking at the following chart for DDR memory, I become confused with some of the information.


I am confused at information regarding the Internal rate, or memory clock speed.
From what I have gathered (correct me if I am wrong) is that, Bus clock speed, is the speed at which the connection between CPU & memory operates at. Higher bus speed means you can send more data more quickly between points (assuming you can process the data more quickly(?)).
Why is it, with the same internal clock speed between DDR & DDR2 (Example: 100MHz) does the DDR2 processes more quickly? I'm well aware of the fact DDR2 is twice as fast as DDR, but why? Why does Bus clock speed effect how fast the RAM actually is? wouldn't bus clock speed just be the maximum throughput capable of that connection? You would still need to increase the speed at which the RAM processes (what I'm under the impression internal clock speed represents), correct? I'm likely misunderstanding some terminology/definition here. I completely understand the relationship between Bus Speed -> Transfers/s -> MB/s -> Module, just having trouble understanding bus speed vs internal speed of ram modules and how and why they effect the module.
 
You cannot just go by internal rate.
DDR and DDR2 might have the same internal rate but DDR2 has double the data rate (MegaTransfers per Second - MT/s)

Imaging a Honda sedan (DDR) and a Ford pickup (DDR2) traveling a the same speed (internal rate).
Which one do you think could haul more cargo?

At the same internal rate DDR2 transfer rate (4.2-6.4GB/s) is twice of the DDR RAM (2.1-3.2GB/s)
 
Last edited:

Karadjgne

Titan
Herald
A better analogy would be 2 Hondas (internal) delivering pizza (data). One Honda speeds, doing 60mph (DDR2 buss clock), the other does 30mph (DDR buss clock) and they both have just 1 hour to make as many deliveries as possible (data rate). The Honda doin 60 will make twice as many deliveries, with the same car in the same amount of time. (transfer rate GB/s)
 

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