DDR - Double Data Rate
DDR2 - Double Data Rate x 2
DDR3 - Double Data Rate x 3
etc...
If your RAM is running at DDR2 1066, it is actually running at 533MHz x 2 since it's "double data rate". Now if your RAM was running at the same speed as your FSB, i.e. 1:1, your FSB would also be at 533MHz.
Lets say you are running your CPU at 3600MHz, being 400MHz FSB with a x8 multi. If you are running your RAM at 1:1 with your FSB here, it will be running at DDR2 800, since it's 400MHz x2. But lets say push your OC farther but your RAM can't keep up with running at 1:1 with your FSB. Lets say you're really extreme and you push your CPU to 5000MHz, 625MHz FSB with a x8 multi; but you have sucky ram so it can't run at 1:1 with your FSB, 'cause it can't run DDR2 1250 (625MHz x2). So you could set it to a divider of say 3:2. So your RAM would be running at DDR2 832, since 625 / 3 = 208(.33333...); 208 x 2 = 416, and then 416MHz x 2 = DDR2 852.
The timings I don't know much about so I can't really explain those, but here it is from good ol'
Wikipedia.
Quote:
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Originally Posted by Wikipedia
RAM Timing
RAM manufacturers typically list the recommended timing for their RAM as a series of four integers separated by dashes (e.g 2-2-2-6 or 3-3-3-9 or 4-4-4-12 and so on). While there are many other settings related to RAM, these four integers refer to the following settings, which are typically listed in this order: CL - TRCD - TRP - TRAS.
CL = CAS Latency time: The time it takes between a command having been sent to the memory and when it begins to reply to it. It is the time it takes between the processor asking for some data from the memory and it returning it.
TRCD = DRAM RAS# to CAS# Delay: The number of clock cycles performed between activating the Row Access Strobe and the Column Access Strobe. This parameter relates to the time it takes to access stored data.
TRP = DRAM RAS# Precharge: The amount of time between the 'precharge' command and the 'active' command. The 'precharge' command closes memory that was accessed and the 'active' command signifies that a new read/write cycle can begin.
TRAS = Active to Precharge delay: The total time that will elapse between an active state and precharge state. This is the sum of the previous timings: CL + TRCD + TRP.
The BIOS on a PC may allow the user to make adjustments to RAM Timing in an effort to increase speed (with possible risk of decreased stability) or, in some cases, increase stability (by lowering the speed).
See dynamic random access memory, specifically the Synchronous Dynamic RAM (SDRAM) section.
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