Please explain memory ratio

[MinhChon]

Someone please explain to me the memory ratio stuff on DDR. I've heard of 1:1, 3:4, 4:3....any others? What is it and why use it?

 

[FluxCapacitor]

This ratio refers to the Front Side Bus (FSB) and the Memory Bus. They both use the PCI system bus of 33Mhz x a multiplier.

For example a ratio of 1:1 simply means you are running the FSB and Memory at the same speed, whatever that might be.
100MHz FSB: 100MHz memory = 1:1
133MHz FSB: 133MHz memory = 1:1
166MHz FSB: 166MHz memory = 1:1

A ratio of 3:4 means you are running your FSB at 33MHz x 3, which equals approximately 100MHz, and your memory at 33MHz x 4 = 133MHz.

3:4 is just an easier way of saying 100MHz:133MHz, provided you know what they are talking about.
The whole reason different ratios exist is so you can run your memory at a different speed from your CPU for improved performance or increased compatibility.

You will also see 4:5, for 133MHz FSB and 166MHz memory, and possibly 5:6 as well.

 

[Budman]

4:5 = +25%
3:4 = +33%
4:6 = +50%
3:5 = +66%
3:6 = +100%


DDR chart. . . . 100fsb . . . 133fsb . . . 150fsb . . . 166fsb
4:5 = +25% . . . 250ddr . . . 333ddr . . . 375ddr . . . 415ddr
3:4 = +33% . . . 266ddr . . . 354ddr . . . 399ddr . . . 442ddr
4:6 = +50% . . . 300ddr . . . 399ddr . . . 450ddr
3:5 = +66% . . . 332ddr . . . 442ddr
3:6 = +100%. . . 400ddr