Overclocking Tutorial
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If you've put together your own system, or bought one from a boutique retailer, you might be interested in squeezing out a little more performance from it. If you've already read articles about the risks of overclocking, and decided that the challenge of overclocking is for you, you're probably eager to get started.
Before we get started, let's remember that different motherboards and processors will work differently; they'll offer different menus and choices, and so on. As a result, it's hard to give a very specific step-by-step guide even for an introductory article. The screenshots here are from the American Megatrends (AMI) BIOS on my Asus P5AD2 Deluxe computer, which uses an Intel Pentium. If you're using a different processor or motherboard, or even a different version of the same equipment, the displays you see might be a little different.
If you're ever unsure of what setting is in question, you should check your manual or ask around in one of the forums. In particular, please join us in the forum if you become intimidated or confused—it's best to ask advice before proceeding to ensure your success.
Meanwhile, let's have a look at how a simple overclock works!
The BIOS
The BIOS setup on your computer is the tool that you'll use to configure the clock speed for your processor. To enter your BIOS program's user interface, you'll want to restart your computer. As it boots, you should notice a prompt like the one below, which invites you to press a key to enter the BIOS. On my machine, that key is DEL -- so I can tap the DEL key in order to get into the BIOS.
Once I'm there, I'm shown the main menu in the BIOS:
I can press the right arrow to move the selection from the "Main" menu to the "Advanced" menu. That changes the options to the ones shown below.
The choices here certainly aren't very self-explanatory. For our first overclock, the setting that interests us the most is "JumperFree Configuration". This selection leads to another menu that will let us change settings that were, about a decade ago, configured with jumpers on the motherboard. Jumpers were very inconvenient and confusing, so manufacturers eventually did away with them and replaced them with software-configurable settings. Many features of your computers BIOS are simply tools that let you adjust those settings without opening the case of your computer moving some jumpers around.
Changing the clock
If I hit ENTER over the "JumperFree Configuration" choice, I see the display below.
Asus motherboards have some settings which allow very easy overclocking. Of course, those same settings hide all of the details from us and don't let us know what they're really doing. It's more fun and education to do it ourselves, so let's proceed. Right now, my "AI Overclocking" setting is "Standard". That means that no overclocking is taking place at all; that my system will run at the standard settings. When the machine boots, the processor will start running the code in the BIOS. The BIOS will turn around and query the processor to see what speed it should be running at; it will use those settings, and that's that.
My processor is a Pentium 4 that runs at 3.2 GHz. That's pretty fast, but it turns out I can get a little more from the processor. How much more? I don't know; part of the process of overclocking is exploring the hardware, finding its limit, and then backing off a bit. To start, let's try to nudge the processor just a little bit faster and see if it works.
To nudge the processor to run a little faster, I'll first change the "AI Overclocking" setting from "Standard" to "Manual". This makes a large list of new options appear on the JumperFree page. Fortunately, this machine and BIOS are relatively easy to overclock; I can leave most of the settings at "Auto" and adjust only one: the CPU Frequency.
When I first set the "AI Overclocking" option to "Manual", the "CPU Frequency" setting was 200. This number is in megahertz and gives the external clock speed for the processor. The machine multiplies it by the FSB multiplier to find the clock rate for the machine. In my case, the FSB multiplier is 16, giving a clock rate of 3200 megahertz, or 3.2 gigahertz.
Let's add just 5 megahertz to the CPU frequency. After I make my change, this is what I see on the Advanced page:
It turns out this adjustment increases my clock to 205 times 16, or 3280 megahertz, or 3.28 gigahertz. Since I started from 3.20 gigahertz, I'm realizing a 2.5 % increase in speed. I can move the selection to the "Exit" page, which looks like this:
Here, I chose "Exit & Save Changes". This commits my changes to the CMOS configuration memory, then reboots my computer. This menu has a couple of other interesting choices. Two of them involve discarding changes". Either one will "forget" my changes and restart the machine. If I become confused, think I've made a mistake, or just want to give up, these are the choices I'll use.
If I find that I've done something drastically wrong, or really believe I've made a mistake, I can choose "Load Setup Defaults". This resets all of my BIOS settings so that I'm at some conservative facotry defaults—settings that won't be too efficient, but are sure to work successfully.
Rebooting
With my change made, I want to reboot my machine. I immediately notice that Windows reports my processor to be running at 3.28 GHz, which means my changes were successful! I can run my Prime 95 and Super Pi tests again and find that everything still works just great. In fact, Super PI completes in 40 seconds. Since Super PI is a processor-intensive test, I know that my speed improvement came from my adjusted clock speed. Success!
Now that I've measured a successful increase, I have a choice. I can shut down my machine and try a little more -- perhaps bumping my CPU frequency another 5 megahertz, or I can call my changes good enough and start using my faster computer. The choice is yours; I'd recommend setting a comfortable goal then getting comfortable with your faster machine. Use it for a few days, at least, in your normal work (or play!) and make sure it's really faster and stable. If you find that it isn't, back off. If it is, consider going a little further.
If I choose to continue, it would'nt be a bad idea to run SpeedFan and monitor the temperatures as a Prime95 test runs. This will let you know if you're getting near the thermial limit of the processor. For the Socket 775 processor I'm using, I don't want temperatures higher than about 65 C. Once they reach that temperature under load, I'll want to investigate a more aggressive cooling solution.
What can go wrong?
Just like anything else interesting enough to try, overclocking can go wrong. One of the first things that might go wrong is that your BIOS might not support overclocking in the first place! Mass-marketed computers often provide a BIOS that's "locked down"—one that does not provide any facility for changing clock speeds. That leaves you with no pleasant choices, really. You can try to upgrade the BIOS to a third-party version which does support overclocking. Or, you can buy a new computer that does provide overclocking capabilities. You might find it best to simply throw in the towel.
Even if your machine does support overclocking, even a conservative first shot at an overclock might be more than your machine can handle. Why does it fail? The causes are situational and the remedies are numerous. Perhaps you have a dirty heatsink and fan which can't get rid of additional heat, a weak power supply, or flakey parts which can't run any faster than their rated maximums. No good generalization exists to explain what might be the problem. Your best be at this point is to find a friendly forum and ask for advice.
If your first overclock is successful, you might actually be disappointed. What if you expected more? We shot for a 2.5 percent performance increase in this article. That's probably going to work, but it's also barely noticeable. A computer that's 20- or 30-percent faster is going to start drawing some attention from the benchmark programs. Even then, the machine's performance is only partially dictated by the processor; faster drives or a faster video card might be more influential in the applications you actually use every day—and they're probably not benchmarks!)
It's also possible that you actually damage your hardware. This warning has been given in many of the articles elsewhere on the site, but if you can't afford to replace it, you shouldn't be bothering with overclocking. It's not a technique for the machine you use to do your taxes or earn a paycheck.
Recovering from the worst
One thing I like to do as I work—whether I'm in the garage working on one of my cars or doing something with a computer—is take notes. I'll jot down my decisions and my last actions. That way, if something goes wrong, I can look at the last change I made, re-read the reasons I had for doing it, and reverse my steps. Even if things are going well, I'm often interrupted. When I'm done with the interruption, I can always look at my notes to remind myself what I was doing. Even if the interruption lasts weeks!
When overclocking, I always make a note of the settings that I change and jot down the results of the benchmark I ran after making them. If I change my CPU Frequency from 240 to 250 and then reboot but find that the reboot fails, I can check my notes and revert to the 240 setting which, according to my notes, worked correctly. This is yet another reason why I recommend an iterative approach: unwinding the last step is easy, and can guarantee success. Now that I know the top spot for this setting is between 240 and 250, I can try a smaller increment; 242, for example, to see if it works.
When you find the limit of your overclock, you might notice any of several symptoms. You could find that your machine boots, shows the BIOS screen, then fails to load Windows. You might find that your testing program fails to complete successfully. You might even find that your testing program appears to work, but your computer is flakey in day-to-day use. Go back to your notes and try the next lowest settings—and keep working backwards until you find something worthwhile.
In a difficult case, you might find that your setting actually causes some corruption and your machine won't boot. You might need to reset the CMOS configuration memory on your machine. There will be specific instructions for this in the manual, but the process usually involves shorting a jumper on the motherboard for a brief period. Some motherboards designed for overlcockers specifically can actually detect a failed overclock attempt and will reset themselves to factory defaults after a second or third failed boot attempt.
If you were lax in your note keeping, you can use the "Load Setup Defaults" command I mentioned earlier. This will reset your BIOS to conservative settings and should allow you to successfully boot your machine.
Summary
A first step at overclocking your CPU can be easy and rewarding. Work slowly, take notes, and monitor your own progress. If you do so, I think you'll find that you're soon comfortable with the idea and are ready to take on the next step!
