This guide has been created from an AMD point of view, but Intel'ers can use this as well.
Warning: Overclocking isn't always safe. There are safety measures built in to your computer to prevent damage while overclocking, but the safety of your hardware isn't guaranteed (even if you are following the guide).
The main pieces in your computer that are affected by overclocking are your CPU, your memory, and your motherboard (but you won't have to worry about your motherboard if you're just beginning to overclock). When you overclock your CPU, you also end up overclocking your Memory, HT link (if you have one), sometimes your AGP/PCI-e and PCI cards, and a few other things. Why? Because of a magical thing called "FSB".
What is FSB?
FSB, as far as overclocking is concerned, is simply a number. Your computer's FSB is the data links between your CPU, Memory, Chipset, and other components. Lots of things in your computer use the FSB to tell it how fast to run. FSB is usually rated in MHz.
How does my CPU use FSB?
Your CPU takes the FSB and multiplies it by the CPU Multiplier to get your CPU speed.
In math? FSB (in MHz) times Multiplier equals CPU speed (in MHz)
How does my Memory use FSB?
Your memory takes that FSB speed, multiplies it by two (DDR=Double
Data Rate), and it gives you your DDR rating.
Sometimes, the processor wants to set the FSB at a high value, but the memory wants to set the FSB at a low value. The motherboard will set a "Divider" that will lower the Memory's FSB so that the Memory can run at the lower speed it wants without affecting the CPU. The Memory Divider is also known as the Memory Ratio.
In math? FSB divided by the memory ratio times two equals DDR Rating.
Why is PC133 so much slower than PC2100. Don't they run at the same FSB?
Yes, they run at the same FSB, but PC133 isn't DDR (and it's older technology).
Wait.. Didn't you say something about a CPU Multiplier? Can't I change that?
Yes. You can change your CPU multiplier, too. Some processors, such as AMD's Sempron, won't let you increase this, though. If you want to overclock your computer, but don't want to change the FSB, you can change the CPU Multiplier. The advantage of changing this rather than your FSB is that the CPU Multiplier only affects the CPU. FSB, like I said before, affects more than your CPU.
Lets make it even more complicated!
Remember FSB? FSB is (and now "was") the link between your CPU, Memory, Chpiset, AGP/PCI-e, and other computer components. As computers started to run faster and faster, a lot of motherboards started getting bottlenecked at these points, so we now have AMD's HyperTransport Technology and Intel's QuadPumped Technology to fix it. Although AMD was the company to bring HyperTransport to fame, AMD, Apple, nVidia, Cisco Systems, Sun Microsystems, and a few other companies all helped develop HyperTransport (HT). HyperTransport links were designed to replace the FSB system. This means that the links between your CPU, Memory, Chpiset, AGP/PCI-e, and other computer components are now three to five times faster than the original FSB system was.
Although HyperTransport was designed to replace the FSB, it hasn't eliminated it. Socket 754's use 4x FSB and Sck939 use 5x FSB. Making your HT Link run faster doesn't make your computer faster, it just gives it the potential to be faster. Making this run too fast will crash your computer.
(Intel plans to release a competitor to HyperTransport that they're calling the Common System Interface (or "CSI"). This is expected in 2008.)
In math? FSB times the HT Multiplier equals the HT Link Speed (or sometimes called "Rated FSB").
Wait! I still don't understand HyperTransport/QuadPumped! And why doesn't it make my computer faster?
The CPU, Memory, Video Card, chipset, and everything else in your comptuer all need to be able to talk to eachother, right? Think of the data paths that link all those things together as highways. If you try to fit too many cars down the highway, you get a traffic jam and some cars have to wait before they can get through. HyperTransport puts more lanes in the highway so more cars can flow through it. If you have two lanes, but only one car is going down the highway, adding a third lane won't make that car go faster. If you have a few thousand cars, but only two lanes, adding a third lane would
make the flow move faster.
What about Intel! Don't they have, like, 1GHz FSB?
Those 800MHz FSB Prescott P4's actually run at 200MHz FSB. Intel also had the same problem with the FSB not being fast enough to support the system. Intel's Pentium 4 line of processors (for example) has their FSB "QuadPumped", which offers the same advantage as HyperThreading. I believe that this is the same story with the "1GHz FSB" Intel processors. If you look at CPU-Z, you should have both FSB and "Rated FSB". For overclocking purposes, we'll only be concerned about the original FSB.
Also, there are rumors that Intel's QuadPumped Technology does not
increase the link speed between multiple processors whereas AMD's HyperTransport does. Given Intel's plan to move to a mainstream Quad Core, a HyperTransport competitor by Intel (aka: Intel's CSI Bus) suddenly makes sense.
I'm a visual learner. Can you show me a picture?
Lets use one that I randomly pulled off of Google's image search.
The image (that should now show up correctly) above represents a Quad Processor AMD Opteron computer (Intel is similar). There is a 6.4GB/s link between each processor and a 6.4GB/s link between the processors and the AMD-8131 Northbridge chipset. The Northbridge connects to the PCI Express bus, SCSI controller, and on-board Ethernet cards. The Northbridge is also connected to the AMD- 8111 Southbridge chipset via a slower 800 MB/s link. The Southbridge connects to slower on-board devices like the on-board audio, USB 2.0, EIDE, etc. This was FSB's job until today's devices became too fast for it. System devices would end up competing for bandwidth. And what shows up like a knight in shining armor? HyperThreading and QuadPumped Technology.
Lets do some math!! Can we have an example?
When stock, my computer runs at 200 FSB. The CPU has a 10x Multiplier. The memory is PC3200 and isn't divided (We call this a 1:1 ratio, or a 1/1 divider). The HyperTransport link runs at a 4x Multiplier. Now that we know all that...
Lets find the CPU speed.
200MHz FSB times 10 (CPU Multiplier) = 2,000 MHz CPU speed, or 2GHz CPU speed.
Lets find the Memory speed.
200MHz divided by 1 times 1 (remember the divider?) times two (Double Data Rate) = DDR400. We can also take that DDR400 and multiply by 8 bytes to give us 3200, or PC3200.
Lets find the HT speed.
200MHz times 4 (the HT Multiplier) = 800MHz HT Link.
Put all that together, and you can see that I have a 2GHz CPU, DDR400 memory, and an 800MHz HT link.
So what happens when you raise the FSB?
Lets say I take my computer and run it at 220 FSB. Lets do the example again.
220 FSB times 10 (Multiplier) = 2,200MHz, or 2.2GHz. (See the increase?)
220 FSB divided by 1 times 1 (1:1 ratio) times two (DDR) = DDR440, or about PC3600
220 FSB times 4 (HT Multiplier) = 880MHz HT Link
At stock speeds, we had:
200FSB, 2.0GHz, DDR400, and 800MHz HT.
Overclocked, we have:
220FSB, 2.2GHz, DDR440, and 880MHz HT
What if you just raise the CPU Multiplier?
Lets say I raise it to 11.
200 FSB times 11 = 2,200MHz, or 2.2GHz.
200 FSB divided by 1 times 1 times two = DDR400 or PC3200
200 FSB times 4 = 800MHz HT Link
200 FSB, 2.1GHz, DDR400 and 800MHz HT
Notice how everything is at it's original speed except the CPU.
Memory dividers are really confusing. Why would I ever want to make my memory run slower? Could you give me an example?
Sure! Lets say your memory runs at 200 FSB, but can only run at a maximum of 210 FSB before it crashes. We can set a Memory Divider of 5/6 to drop it down from 200 FSB to 166 FSB. Now we can raise your FSB higher without stressing out your memory as much.
200 FSB divided by 6 times 5 times two = DDR333
240 FSB divided by 6 times 5 = DDR400 (Back to where we started, but the FSB is a lot higher and the memory is still in a safe range.)
How do I know when to stop?
When your computer will not boot in to Windows (or if it does, will freeze after a few minutes of gaming), you'll know that you have pushed something too far. If you've overclocked to the point where your computer unstable, you can boot into the BIOS and set your FSB back down. If you overclock too far your computer may not boot at all. If your computer does not do anything when you turn it on, you'll need to reset the BIOS. You can do this by unplugging your power cable and removing the silver button battery on your motherboard. Leave it out for at least 5 seconds (15 seconds recommended) and then put it back in. Plug in the power cable and boot. You'll need to go into your BIOS and load the default settings.
An alternative to changing the FSB in the BIOS is to change the FSB with a program such as ClockGen
. When your computer crashes, the actual BIOS value doesn't change, so you reset to stock speeds every time you reboot. Once you've found an overclock that works for you, you can try setting it in the BIOS.
Another thing that could stop your computer from running (and could potentially damage your computer) is heat. Overclocking means more power. More power means heat
. If your CPU, Memory, or motherboard chipset(s) become too hot, they will stop working properly. Overclocking is not recommended on stock CPU coolers. While overclocking, always watch your temperatures!
If something becomes too hot, do anything you can to cool it down before you try overclocking again. Most things can be easily cooled by simply adding a fan to blow over it.
I can't raise my FSB anymore! Is this really as fast as my computer will ever go?
The exciting answer is "No"! Just because your computer has hit it's limit doesn't mean that everything
in your computer has hit it's limit, but rather that one thing
in your computer has hit it's limit. If you can figure out what thing that is, you can usually make that one thing run a little slower. For example, if your memory is what's crashing but your CPU can run faster (this is common), you can use the Memory Divider to lower it. With the memory running a notch slower than usual, you can increase your overclock even more.
You'll need to learn a lot more about overclocking if you want to go to the extremes that you see in "The Extreme OC Clubhouse"
How can I check what my computer is running at now?
Try using CPU-Z
. CPU-Z will let you look at all the fun little numbers that make your computer tick without running the risk of accidentally changing something.
Okay! I'm confident that I know what I'm doing. Where do I change my FSB?
Your FSB (and everything else to do with overclocking) is located in your BIOS. Be careful, though. There are a lot of settings in here that shouldn't be played with. Different motherboards will have the FSB in different places. If you can't find your FSB, it may be disabled from the BIOS. You can try asking people in the forums, but each BIOS is unique to their manufacturer. If all else fails, try using ClockGen
. ClockGen runs inside Windows and can support a good range of motherboards.
If you have any questions, ask!