Unless your overclocking you can completely ignore this because your multiplier will be set up automatically.
Ram chips, like CPU chips, are sold on their rated speed. DDR2-800 actually operates at 400 MHz, this is because ram transmits their bits on the rising and falling edge of the clock (similarly, DDR2- 667, actually operates at 333 Mhz, and DDR2-533 will operate at 266 MHz.
The FSB clocks itself by quad pumping the system clock, the memory clocks itself by a ratio of this clock (what you call FSB : DRAM), the CPU clocks itself by a multiplier x the system clock.
Since Intel (or AMD for that matter) fix the system clock for any particular generation, then to make all the different RAMs compatible, the RAM must be 'divided'. For example, to Run DDR2-800 at the rated 400MHz on a C2D stock system, the system clock of 266 must be multiplied by 3 then divided by 2 or a ratio of 3:2. This would convert the system clock to 400 MHz and send data at DDR2-800 speeds. As another example, DDR2-533 is clocked at 266, so it is a 1:1 match for the stock 266MHz. If you overclock to 333 MHz for example, DDR2-533 would likely fail as this is now significantly above it's rated speed.
Keep in mind that Gigabyte has a simplified BIOS, instead of using the 1:1 ratio, or 3:2 ratio, it'll say 2x or 1.5x multiplier. however as of now, Gigabyte doesn't support a multiplier lower then 2. If you don't understand this, there really is no better way that I can explain it and you'll have to go and do a little research on the topic, again if you don't plan on overclocking, there is no need to worry about this.
Hope that clears it up.
Edited by james_8970, 02 November 2007 - 09:35 AM.