RAM and what it has to do with Overclocking
As I said before, the FSB is the pathway through which your system communicates with your CPU. So raising the FSB, in effect, overclocks the rest of your system as well.
The component that is most affected by raising the FSB is your RAM. When you buy RAM, it is rated at a certain speed. I'll use the table from my post to show these speeds:
PC-2100 - DDR266
PC-2700 - DDR333
PC-3200 - DDR400
PC-3500 - DDR434
PC-3700 - DDR464
PC-4000 - DDR500
PC-4200 - DDR525
PC-4400 - DDR550
PC-4800 - DDR600
Note how the RAM's rated speed is DDR PC-4000. Then refer to this table and see how PC-4000 is equivalent to DDR 500.
To understand this, you must first understand how RAM works. RAM, or Random Access Memory, serves as temporary storage of files that the CPU needs to access quickly. For instance, when you load a level in a game, your CPU will load the level into RAM so that it can access the information quickly whenever it needs to, instead of loading the information from the relatively slow hard drive.
The important thing to know is that RAM functions at a certain speed, which is much lower than the CPU speed. Most RAM today runs at speeds between 133MHz and 300MHz. This may confuse you, since those speeds are not listed on my chart.
This is because RAM manufacturers, much like the CPU manufacturers from before, have managed to get RAM to send information twice every RAM clock cycle.* This is the reason for the "DDR" in the RAM speed rating. It stands for Double Data Rate. So DDR 400 means that the RAM operates at an effective speed of 400MHz, with the "400" in DDR 400 standing for the clock speed. Since it is sending instructions twice per clock cycle, that means it's real operating frequency is 200MHz. This works much like AMD's "double pumping" of the FSB.
So go back to the RAM that I linked before. It is listed at a speed of DDR PC-4000. PC-4000 is equivalent to DDR 500, which means that PC-4000 RAM has an effective speed of 500MHz with an underlying 250MHz clock speed.
So what does this all have to do with overclocking?
Well, as I said before, when you raise the FSB, you effectively overclock everything else in your system. This applies to RAM too. RAM that is rated at PC-3200 (DDR 400) is rated to run at speeds up to 200MHz. For a non-overclocker, this is fine, since your FSB won't be over 200MHz anyway.
Problems can occur, though, when you want to raise your FSB to speeds over 200MHz. Since the RAM is only rated to run at speeds up to 200MHz, raising your FSB higher than 200MHz can cause your system to crash. How do you solve this? There are three solutions: using a FSB:RAM ratio, overclocking your RAM, or simply buying RAM rated at a higher speed.
Since you probably only understood the last of those three options, I'll explain them:
FSB:RAM Ratio: If you want to raise your FSB to a higher speed than your RAM supports, you have the option of running your RAM at a lower speed than your FSB. This is done using an FSB:RAM ratio. Basically, the FSB:RAM ratio allows you to select numbers that set up a ratio between your FSB and RAM speeds. So, say you are using the PC-3200 (DDR 400) RAM that I mentioned before which runs at 200MHz. But you want to raise your FSB to 250MHz to overclock your CPU. Obviously, your RAM will not appreciate the raised FSB speed and will most likely cause your system to crash. To solve this, you can set up a 5:4 FSB:RAM ratio. Basically, this ratio will mean that for every 5MHz that your FSB runs at, your RAM will only run at 4MHz.
To make it easier, convert the 5:4 ratio to a 100:80 ratio. So for every 100MHz your FSB runs at, your RAM will only run at 80MHz. Basically, this means that your RAM will only run at 80% of your FSB speed. So with your 250MHz target FSB, running in a 5:4 FSB:RAM ratio, your RAM will be running at 200MHz, which is 80% of 250MHz. This is perfect, since your RAM is rated for 200MHz.
This solution, however, isn't ideal. Running the FSB and RAM with a ratio causes gaps in between the time that the FSB can communicate with the RAM. This causes slowdowns that wouldn't be there if the RAM and the FSB were running at the same speed. If you want the most speed out of your system, using an FSB:RAM ratio wouldn't be the best solution.
Overclocking your RAM
Overclocking your RAM is really very simple. The principle behind overclocking RAM is the same as overclocking your CPU: to get the RAM to run at a higher speed than it is supposed to run at. Luckily, the similarities between the two types of overclocking end there, or else RAM overclocking would be much more complicated than it is
To overclock RAM, you just enter the BIOS and attempt to run the RAM at a higher speed than it is rated at. For instance, you could try to run PC-3200 (DDR 400) RAM at a speed of 210MHz, which would be 10MHz over the rated speed. This could work, but in some cases it will cause the system to crash. If this happens, don't panic. The problem can be solved pretty easily by raising the voltage to your RAM. The voltage to your RAM, also known as vdimm, can be adjusted in most BIOSes. Raise it using the smallest increments available and test each setting to see if it works. Once you find a setting that works, you can either keep it or try to push your RAM farther. If you give the RAM too much voltage, however, it could get fried.
The only other thing that you have to worry about when overclocking RAM are the latency timings. These timings are the delays between certain RAM functions. If you want to raise the speed of your RAM, you may have to raise the timings. It's not all that complicated, though, and shouldn't be too hard to understand.
That's really all there is to it. If only overclocking the CPU were that easy
Buying RAM rated at a Higher Speed
This one's the simplest thing in this entire guide If you want to raise your FSB to, say, 250MHz, just buy RAM that is rated to run at 250MHz, which would be DDR 500. The only downside to this option is that faster RAM will cost you more than slower RAM. Since overclocking your RAM is relatively simple, you might want to consider buying slower RAM and overclocking it to fit your needs. It could save you over a hundred bucks, depending on what type of RAM you need.