Detailed Ram Info? DDR2 2:3, 5:6

[parthibangemini]

Do any of you know what is the difference between the two type of Rams, both are same DDR2 800MHz 2GB ram of same company specifically Transcend. why there is a change in the memory frequency 2:3 and 5:6 what are those.
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DDR2 Transcend 2048 MBytes PC2-6400 (400 MHz)
Channels - Single
Memory Frequency 400.0 MHz (2:3)
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DDR2 Transcend 2048 MBytes PC2-6400 (400 MHz)
Channels - Single
Memory Frequency 400.0 MHz (5:6)
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And nowadays Rams are only half the size of the original? why? any change in speed, heat?

[whisk3rs]

I don't claim to understand it myself, but I believe this ratio is called the divider. http://en.wikipedia.org/wiki/Memory_divider

I believe it's useful for overclocking.