RAM related queries

My ProBook 4520s has a 2GB DDR3 RAM. Using a hardware information application software (PC Wizard) I got the following information regarding the installed RAM -
DDR3-SDRAM PC3-10700 (667MHz) – [DDR3-1333]

As per my understanding it’s BUS speed is 1333MHz and data transfer rate is 10700MB/s.
So, what is the significance of 667MHz? Is it the max. supported BUS of the motherboard? The installed RAM has much higher BUS but as motherboard supports till 667MHz the RAM is performing with 667MHz?

Could anybody please clarify this thing?

 

667 MHz is the actual speed. Since it is DDR (double data rate) the effective speed doubles and hence 1333 comes from.

Similarly my DDR2-800 rams run at 400MHz actual speed.

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My desktop's RAM is DDR2-SDRAM PC2-6400 (399MHz) – [DDR2-800]

So, actual speed is 399MHz (400MHz). As it is DDR, effective speed is double i.e., 800MHz.

But what is the difference between DDR2 and DDR3?

 

Max possible clock speeds and voltage used fo the RAM for example. DDR3 runst at 1.5V, DDR2 runs at a higher voltage (1.8 i tihnk). This means that the RAM will run cooler at the same frequencies, thus allowing higher frequencies without producing too much heat.

 

DDR3 can do 8 transfers per clock cycle, and DDR2 can only do 4. As a result the effective frequency of DDR3 is double DDR2 at the same base clock rate. DDR3 is made all the way up to 2100 Mhz, while DDR2 only goes up to 1066 Mhz.

 

Incorrect, i had 2200MHz Geil RAM on my desktop.

 

Let's think about two RAMs-
1. DDR2 800MHz (actual 400MHz, effective 400*2=800MHz)
2. DDR3 1333MHz (actual 667MHz, effective 667*2=1333MHz)

In both the cases we made double of the actual clock to get effective speed. But how can we realize 8 transfers per clock cycle for DDR3 and 4 for DDR2?

 

This article might interest you, it was written when DDR3 was first being released to market a few years ago: AnandTech - DDR3 vs. DDR2.