If you want to squeeze every last ounce of processing power out of your new computer or aging system, overclocking is a great — if slightly nerve-racking — option. Here are some simple guidelines for safely overclocking your CPU.
Photo by blazor85.
Simply put, overclocking your CPU involves running your processor at a faster speed than was intended out of the box. While overclocking at its core (no pun intended) can be quite simple, there's a bit more to it than just tweaking one setting. The main setting that determines your CPU speed (known as your Base Clock) also affects your RAM speed, so there's a bit of tweaking required to get the right balance. You'll also have to tweak a few voltage levels, because without enough power, the CPU can't run fast enough. However, higher voltage also means higher temperatures, so you need to be careful not to overheat your CPU, which can lower the life, not to mention fry it completely if you're not careful.
This particular guide was written with the Intel i7-930 "Bloomfield" processor on a Gigabyte GA-X58A-UD3R motherboard, though most of the basic ideas behind it can apply to other, similar processors (such as the Lynnfield i5s and i7s) and other compatible motherboards. I highly recommend doing extra reading, even if you have the same gear as me, and especially if you have different gear. No two systems are the same, and overclocking is not something to be taken lightly. I wrote this guide from my experience, but I had a lot of help from sites like overclockers.com, overclock.net and hexus.net, to name a few. At the end of this guide I've provided links to a few specific guides that should provide more information, and I highly suggest you check them out. Also do some forum browsing and googling for more information on subjects you don't understand or that we don't cover in depth. All that said, this guide should put the process into basic enough terms that those unfamiliar with overclocking can get a general feel of what it entails and how to get started overclocking their systems.
There are any given number of reasons one would want to overclock, but in general, you'll get the most benefit if you're using your computer for more CPU intensive tasks, such as gaming or video encoding. Of course, many overclockers simply enjoy the thrill of playing around with their systems and pushing it to the limit (or at least pushing it further), so if that's reason enough for you, then go for it. Know, however, that overclocking can be dangerous and can shorten the life of or permanently damage some of your components if something goes wrong, so don't start tweaking unless you're prepared to face the potential consequences.
Note: I'm being particularly doomsday here to emphasise that things could go wrong. If done correctly, overclocking is generally a pretty safe endeavour (I've never damaged my gear), but if you're not willing to risk damaging your processor, you may want to skip it.
While this is not an exhaustive list, these are the settings we'll be tweaking in this guide. The jargon related to your clock speed is as follows:
- The Base Clock affects both your CPU frequency and RAM frequency as described below. This is one of the main settings we'll be focusing on in this tutorial.
- Coupled with the base clock, your CPU multiplier decides your final CPU frequency. It works like this: if your base clock is, say, 133 MHz (the default of the i7) and your multiplier is x21, your CPU frequency will be 133 MHz x 21 = 2.8 GHz.
- The RAM multiplier is very similar. The same base clock of 133 MHz coupled with a RAM multiplier of 8 will give you about 1066 MHz.
- Uncore frequency is another multiple of the base clock, and basically affects the speed of everything that isn't the core. Your only goal with the uncore frequency is to keep it at a 2:1 ratio with your RAM speed, so any time you edit your RAM multiplier, you'll have to double check your uncore frequency to keep your system stable.
As far as voltages go, these are the ones you'll want to be familiar with:
- CPU Vcore is directly related to your CPU frequency. You will likely have to raise it as you raise your CPU multiplier.
- QPI or Vtt voltage will help you keep your system stable as you raise the base clock.
- DRAM or VDIMM voltage is the voltage provided to your RAM. For this guide, you probably won't have to raise this, but if you do, make sure it doesn't go more than .5 volts above your QPI/Vtt voltage.
- IOH voltage is the voltage supplied to your PCI cards. You'll probably set it once and leave it there, depending on how many graphics cards you have.
What You'll Need
- A Windows machine. This guide is for Windows, though if you have a Hackintosh or a Linux machine with a Windows partition, that should do fine — we're just going to do our stability testing in Windows.
- An Intel i5 or i7 processor. Again, this guide was written with the i7-930 Bloomfield, though Lynnfield i5s and i7s should follow similar processes. The Clarkdale i3s and i5s are a bit more complicated as the GPU is also thrown into the mix, so I suggest you do some extra reading on guides made specifically for those processors (This guide , for example, has some helpful notes). Though again, do some outside reading even if you have the Lynnfield processors, as each model has its own idiosyncrasies.
- Prime95. This program was made to calculate prime numbers, and has become the standard for stress testing your CPU. It will consistently load your CPU to 100%, helping you decide whether it's stable and cool enough to run regularly.
- Previously mentioned RealTemp. This program will help you monitor your CPU temperature as you run Prime95, so you know if your CPU is getting too hot.
- Previously Mentioned Memtest86+. This is a small boot CD that we'll run just to make sure your memory is stable once you raise the base clock.
- A good cooling system. If you plan on overclocking more than just a little bit, you'll want to get something other than the stock Intel heatsink and fan. This is the heatsink and fan I use, and it's served me quite well. Of course, if you have the cash, you can spring for water cooling and get even lower temperatures (and thus higher overclocks). Ask around, read reviews on Newegg, and think about your overclocking goals to decide what kind of cooling you want.
Here I will outline the basic steps to getting a stable overclock on your system. This particular process is longer than what most guides suggest, but I've found that it's much easier to get everything stable if you only change one thing at a time, rather than setting your clock speed and guessing which voltages you need to raise. This process is pretty time consuming, so find something to do while you test, because you'll be doing a lot of restarting and waiting around.
Editing the BIOS is fairly easy. To change a setting, just highlight it with the arrow keys and press enter to see your BIOS' predefined values for that setting. Alternatively, you can just highlight a setting and start typing in a number, and your BIOS will usually show you the predefined values in a small window to the left. Some settings cannot be edited by default, and you may need to look at the option above them to enable tweaking of that feature. Note also that some settings will be in submenus, usually defined by having a "press enter" option instead of a value next to them.
We're going to spend most of our time in what my BIOS calls the "MB Intelligent Tweaker", though your motherboard may call it something different. In addition, your pictures may not look exactly like mine, but they should give you a general guideline as to what is what. Apologies for the slightly bad quality pictures; it's difficult to take screenshots of the BIOS so they are just photos. You can click on any of them to get a closer look.
Set a Goal and Prepare Your BIOS
Since we can't just jump right up to our desired speed, it's important to have some sort of goal in mind before we begin. Think of why you're overclocking and what kind of final speeds you'd like to see out of your computer: whether it's just a little bit (say, bringing a 2.8GHz i7 up to 3.5GHz) or whether you'd like to crank it up pretty high (say, up to 4 or 4.2GHz). Keep in mind that these numbers are relative; if you've got an i5 or an i3, your goals will be a bit lower. Now, with that goal in mind, think of what base clock you'd need to make that happen with a multiplier of x19 or x21, since your multipliers will generally be in that area, and x20 tends to be unstable.
So, for example, my goal was to make it to 4GHz, which is pretty lofty, but doable. Thus, the base clock I'm aiming for would be around 210 MHz — I could either go with 190MHz with a multiplier of 21 or 210MHz with a multiplier of 19 to reach 3.99GHz. I opted for the former, but made 200MHz my base clock goal just so I'd have a bit of wiggle room at the end.
If you've messed with your BIOS at all, reload the default settings before beginning. If there are any settings you need enabled (like legacy drivers for USB keyboards), set those now. There are also a few settings we'll want to disable before we start overclocking. First, you'll want to disable anything related to Turbo Mode as this will give you a higher clock speed than you define, and we want to know exactly where our processor is, speed-wise. Also turn off any power-saving settings such as EIST, C1E, and other C-state support for now. I would also turn off Load Line Calibration. Both the power-saving settings and Load Line Calibration are a bit controversial — many people say you can turn these back on after you're done overclocking, while others prefer not to. Do some extra reading on the debate and make a decision for yourself — for what it's worth, I've got them all re-enabled right now and I have yet to have issues, but my overclock is still young, so that may change.
Lastly, turn to your RAM. We will not be overclocking RAM in this guide, but we will still need to tinker with it a bit. A lot of times, your RAM doesn't even run at stock by default, so we'll make sure we get them up to speed. Before starting, we'll need to set your RAM timings according to your manufacturer. To find your manufacturer's recommendations, find your RAM on Newegg (for example, this is mine) and click the specifications tab. Under "timing", you'll see a string of numbers, such as 9-9-9-24-2N. This refers to the CAS Latency Time, tRCD, tRP, tRAS and Command Rate, respectively. So go into your BIOS and enter in your manufacturer's numbers for these features (you may need to do it separately for each channel). Also make sure you set your DRAM voltage to that defined by your manufacturer, in this case 1.5. When you're finished, your screen should look something like this:
If everything looks good, it's time to start adjusting the base clock.
Isolate and Stabilise Your Base Clock
The first step is to make sure your base clock can reach your desired goal. The best way to do this, I've found, is by turning everything else down so we can focus on one thing at a time. Turn your CPU multiplier down to something low, like x12, and put your RAM multiplier on its lowest setting, usually 6 (sometimes also displayed as 2:6). Since we've edited the RAM multiplier, we'll also have to change the uncore frequency, so set it to x12 (double your RAM multiplier of 6). This will keep your system stable.
Now go back to the tweaking screen and go down to your voltage section. Set your IOH core to 1.3 if you have one PCI card, or 1.35 if you have two (some motherboards don't have this setting, in which case just skip this step). Set your Vcore and QPI/Vtt voltages to their normal numbers (which should be listed next to them); just be sure to take them off Auto. Everything else can be left as-is for now. Lastly, increase your base clock from its normal setting by 10 or 20 MHz. Then, save your BIOS settings and exit, restarting your computer. Boot into windows and start up CoreTemp.
At this point, lots of people also like to run CPU-Z to make sure their settings were applied correctly, though I find that it just gets in the way. It's up to you.
Next, start up Prime95 and set it to do a Blend test. Hit OK and let it run for about five minutes. Your temperatures probably won't be too high in this stage, but keep an eye on them anyway. The hottest temperatures you want to reach while running Prime95 are up to you, though I like to keep it under 30C or so.
After five minutes, if Prime is still running, go ahead and restart back into the BIOS. Bump up your base clock by another 10 MHz and run through the process again. If Prime95 threw you an error, or if your computer froze, restarted or gave you the BSOD (Blue Screen of Death), go back into your BIOS and raise the QPI/Vtt voltage by one increment and run the test again. Repeat this process until you reach your base clock goal or until you reach unsafe temperatures (which again, you're unlikely to do in this stage). If you're running your desired base clock at and it's handling a few minutes of Prime95 without error, run it for an hour or so instead of five minutes, raising the voltage if need be. Once it's stable for an hour of Prime95, move on to the next step.
Stabilise Your Memory
Now that your base clock is where you want it to be, you'll want to get your RAM running at or near stock speeds. Your stock speed will be listed on the Newegg page for your RAM, generally in the title after its DDR type. My RAMs speed, for example is 1600 MHz (listed as "DDR3 1600"). At this point in my testing, my base clock was 200, so setting my RAM multiplier to 8 would give it the stock speed of 1600 (200 base clock x 8 = 1600). You may not be able to get it exact with your chosen base clock, so just get it as close as you can for the purposes of this (remember, we're not going to talk about overclocking RAM today, so the goal is to just get it close). Don't forget to reset your uncore frequency as well, to make sure that it is twice your RAM speed.
Once everything is set, reboot your computer with the Memtest86+ disc inserted (make sure your BIOS is set to boot from CD before booting from the hard drive). As it starts up, choose option 1 and it will automatically begin testing. It should make it through one cycle without a problem since we're not overclocking. If it throws you an error, try raising the DRAM voltage (but be careful not to raise it more than 0.5 volts above your QPI/Vtt value). If it still isn't stable, you might be one of the unlucky few that can't run your RAM at its stock speeds, so go back and lower the multiplier again (and uncore frequency) to see if that helps. If you're still having problems after a bit of tweaking, you may have a defective stick of RAM that went unnoticed until now. Once your RAM passes Memtest, reboot into your BIOS for the last step.
Adjust Your CPU Multiplier
Now it's time to get your CPU running at your desired frequency. Everything else at this point should be stable, so you just need to adjust the CPU multiplier and the Vcore voltage. Leave the Vcore where it is (it should still be running at the "normal" speed defined by your board), and raise your multiplier by a few levels. Run the Prime95 test again as previously described, though keep a closer eye on your temperatures as they may start to get pretty high in this phase. If everything checks out after a few minutes, restart into your BIOS and raise your multiplier again. If the test fails, reboot into your BIOS and raise your Vcore by one increment and run the test again. If your temperatures get too high (into the mid to high 80s), you either need to get a better cooling system or settle for a lower overclock.
If you reach your desired clock, then you're in the home stretch. You may have to do a bit of fiddling at this point to get to the clock you want (200MHz was my goal base clock, but I'm actually running it at 190 right now to get a 190 x 21 = 3.99 GHz clock speed). Once everything looks good, you'll need to put it through some more rigorous testing: run Prime95 for anywhere from 6 to 12 hours, and see if it passes. If not, raise the Vcore a bit more and try again. Once you can run Prime95 for 6 hours or more without an error, you've got yourself a pretty stable overclock. I like to test it in more practical situations as well, just to make sure — i.e., if you're a gamer, play a little Crysis; if you're a video encoder, throw a Blu-Ray at Handbrake and see if it runs without error. If everything checks out, then congratulations! You have successfully overclocked your system.
There's plenty more to overclocking, but this guide should be enough to keep any beginner busy for awhile. Remember to do some outside reading; the sites mentioned at the beginning of this article have a ton of information contained within. In particular, I had a lot of help from these specific guides, and I recommend you take a look at them as well:
- 3 Step Guide to Overclock Your Core i3, i5, or i7 - Overclockers.com
- i7 Overclocking for Beginners - Hexus.net
- Ultimate Core i7 Overclocking Guide - MaximumPC
- Guide to Overclocking the Core i7 920 or 930 to 4.0GHz - Overclock.net
Some of these are processor-specific, but you should be able to find similar guides for yours with a bit of googling. I highly recommend looking at these anyways, as well as other articles they link to, because there's some really good information in there about some of the more contested settings, as well as the background information on how it all works.
A few things to keep in mind: Everyone's system is different. Overclocking forums can be extremely helpful as far as general information, but just because someone clocked their system to 4.5GHz does not mean you can do the same, even if you have nearly identical gear. Sometimes, these posts can be helpful for pointing out other settings we haven't covered, but in general, this method will get you where you need to go. Of course, everyone does things a little bit differently, and some of you have probably overclocked your fair share of systems, so feel free to share your thoughts, methods, and tips in the comments.