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How To Overclock an AMD Athlon X2

written by: M.S. Smith•edited by: J. F. Amprimoz•updated: 6/6/2009

AMD's Athlon processors may be old news, but they're also one of the longest lasting, most popular product lines to ever hit the CPU market. If you've got one of these old soldiers and want to give it a fighting chance against today's bigger, meaner processors, then look no further.

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    Life From The Old Bird

    Athlon's X2 processors are old. The architecture they're based off was first introduced not long after the turn of the century. But AMD has milked a lot of life out of its old architecture by gradually increasing clock-speeds, lowering thermal footprints, and lowering prices. Even today, Athlon's entire X2 line-up remains a strong contender in the sub-$100 dollar processor market, particularly when AMD's better low-end motherboard chipsets are considered. If you have less than $100 to spend on a motherboard, it's hard to find a good Intel board, but it will take you into the mid-range of AMD's boards.

    The downside to the Athlon X2 is that if you currently have one, you may find yourself at the end of the road, in terms of upgrades. Even the fastest Athlon X2 processors do not compete well with true performance processors like the Phenom II and Core 2 - nevermind Core i7. And unfortunately, many older Athlon X2 processors sit on motherboards that don't support the best Phenom processors due to the high power requirements.

    If Phenom II would take a whole new motherboard, getting the most from your Athlon is crucial. This, of course, is where overclocking steps in. Athlon X2 processors can certainly achieve overclocks of 25%, if properly cooled. Also, if you have a low-end Athlon X2, upgrading to a "Black Edition" processor may be a good idea, as those processors can be overclocked substantially and feature an unlocked multiplier, which I will explain later.

    A warning - overclocking always runs the risk of damaging hardware, and overclocking also voids the warranty on your processor. Keep these risks in mind when overclocking your processor.

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    What You Need

    The only thing that you must, without exception, have when overclocking is a motherboard that includes BIOS options for overclocking. This includes the ability to adjust the Reference Clock, the CPU Multiplier, the Hypertransport Multiplier, the Northbridge Multiplier, and the Memory Multiplier. You do not necessarily need access to all of these options in order to overclock, but you at least need to be able to adjust the Reference Clock, and access to all of these options is required to reach the highest overclock possible.

    Determining if your motherboard has a BIOS which allows these changes can be done either by consulting the manual of your motherboard or by exploring your BIOS. Most BIOSes which have serious overclocking support are going to lump these controls in a specific category, which can be accessed from the main BIOS menu. Unfortunately, there is no standard which says what these controls must be called, so having a motherboard manual to reference is useful.

    There are no other requirements for overclocking. For reaching a maximum overclock, having a processor with an unlocked CPU multiplier, RAM with room for overclocking, and a good cooling solution are all good idea. However, if you don't already have these items, you shouldn't buy them unless you're more interested in reaching the highest overclock possible then getting the best value out of your current hardware.

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    AMD's Athlon X2 processors are unique in that it is easy to get a hold of one that has an unlocked multiplier without having to sell your kidney. Having an AMD processor with an unlocked multiplier makes overclocking easy, because all you need to do is adjust the CPU multiplier. Without the unlocked multiplier, making adjustments will require you to adjust the Reference Clock, as well as the multipliers for the Northbridge, Hypertransport link, and Memory. Athlon X2, Overclocking
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    Overclocking Via The CPU Multiplier

    Restart your computer and boot into BIOS. On most computers, this is achieved either by holding down DEL or F12. If successful, the BIOS will appear on your screen rather than the normal Windows loading screen. Find the menu which controls overclocking, either by consulting your manual or exploring the BIOS, and then open that menu. You should arrive at a BIOS screen full of options.

    The first thing you should attempt to adjust is the CPU multiplier, provided you have an AMD processor with an unlocked multiplier. Adjusting the CPU multiplier makes overclocking very easy, because you don't need to touch the Reference Clock. The problem with adjusting the Reference Clock is that it also changes the speed of your Hypertransport link, your Northbridge, and your Memory, thus adding three additional components which may not be able to tolerate the burden of overclocking. Adjusting the CPU multiplier puts the overclocking load on your processor alone, however.

    As always when overclocking, it is best to adjust in the smallest steps possible. Bump up the multiplier by either .5 or 1, save your settings, then reboot all the way into your operating system. Continue this until you start to experience instability, and then back down until you can boot without any freezes, blue screens, or automatic restarts. You've just overclocked your processor. Simple, right?

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    Overclocking Via Reference Clock

    If you don't have access to an unlocked multiplier, things are a little more complex. You'll need to overclock by adjusting the Reference Clock. This can be a problem, because the Reference Clock also affects the speed of your Hypertransport link, your Northbridge, and your Memory. So, by adjusting your Reference Clock, you will also be adjusting the speed of all of these components. You're no longer relying simply on the potential of your processor.

    Overclocking also becomes more complex because again, motherboard manufacturers don't have a standards regarding the designations they give to the options that allow overclocking. I've seen motherboards which call the Reference Clock the Front Side Bus, for example, although AMD Athlon X2 processors do not actually have a Front Side Bus. Again, having a motherboard manual to reference to is very handy, as it will help you decode what specific settings your motherboard's BIOS uses for overclocking.

    Whatever your motherboard's BIOS, there are a few things you can expect to see. First off, most motherboards will have some sort of overclock master control that will need to be set to Manual or Disabled, instead of Normal or Turbo, so that you can tweak the overclockin options by hand. Secondly, the Reference Clock should also be listed as 200Mhz stock, so if you see a setting listed as 200Mhz, it is a candidate to be the Reference Clock. Northbridge and Hypertransport are both often reduced to NB and HT, respectively. Finally, Memory configuration is usually kept somewhat separate from the other multipliers - if you see an area that allows you to change DRAM timings and DRAM voltages, you're in the ballpark.

    You'll now need to find the limit of your Reference Clock. To do this, lower all available multipliers between the Reference Clock and Northbridge, Hypertransport, and Memory to the lowest settings possible. Then begin bumping up the reference clock in 5mhz increments. This will increase the speed of your processor as well, because your processor's speed is determined by the Reference Clock multiplied by the CPU multiplier (the multiplier you didn't lower, and may have raised in the first step on this page). Keep increasing until you have instability when booting. Then back down. You've now found the limits of your Reference Clock in combination with your processor.

    This is where things become complex. Because the Northbridge, Hypertransport link, and Memory all can be adjusted separately, you'll need to test each in combination with your maximum Reference Clock to see how far you can push your computer. Take it one at a time, increasing until you find instability with one multiplier, then back down a step on that multiplier and attempt to increase another. There is a lot of trial and error to be done here, but with some time you'll be able to find a comfortable overclock.

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    Overclocking provides you maximum bang for the buck, no matter if you're buying new or used. Even if you can only overclock your processor by 10% - which would be quite low - you'll still be getting a performance gain without having to put any into your system. Older AMD Athlon X2 processors are a good choice for overclocking, particularly if you have a Black Edition AMD processor with an unlocked multiplier. But in either case, you should be able to squeeze a little more life out of your existing AMD processor.Athlon X2, Overclocking
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    Pushing The Overclock

    Once you've found the maximum overclock, you can attempt to push things further by adjusting the voltage of your processor. This sometimes helps because as a processor runs faster, it also needs more power. Processors have stock limits on how much power they can bring in, and if your processors is set to take in too little voltage for the speed you're running it at, it will become unstable.

    Increasing voltage should always be done in small steps, preferably in increments of .025 or less. This is simply because voltage increases are the most dangerous part of overclocking. Since you are increasing the amount of power sent into your processor, you run the risk of frying it if you send in far to much. Also, keep in mind that all voltage increases run the risk of reducing overall processor life, and of voiding your warranty should the processor be fried. So take it easy, and keep voltage increases within a limit of 10% above stock.

    Besides the processor voltage, it is also possible to increase the Northbridge voltage. This can be helpful if you are adjusting via Reference Clock, and you believe that your Northbridge's ability to overclock is limiting the potential of your overclock. As with the processor, be careful when doing this, and increase only in small steps. Much as you can track down manufacturer information on CPU voltage, you can try to find similar information on the motherboard manufacturers's websites or support forums.

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    When Things Go Wrong

    The most frightening thing that can, and probably will, happen when overclocking, is a computer that will not boot. In some cases, the processor or motherboard will simply choose to shut down when pushed too hard. The result is a computer that does not boot. Advanced overclocking motherboards include features that will automatically load fail-safe defaults in the event of such a failure, but less intelligent hardware will simply sit.

    Don't panic. Overclocking always holds the potential for harming your hardware, but as long as you're increasing your overclocks in small steps and you're not making wild voltage adjustments, you hardware is likely fine. All you need to do is reset your BIOS to default, so that your computer will boot. Resetting your BIOS is simple.

    That said, if resetting the BIOS does not work, then it is very possible that some hardware in your PC has bought the farm. Your main task at that point should be determining what has gone wrong. It is likely the processor or the motherboard, and the easiest way to tell which is to slip in a different processor and see if computer boots. Just remember to reset the BIOS before doing this, or your motherboard might fry the new processor.

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    Checking Long-Term Stability

    Once you have an overclock that allows you to boot into your operating system without issue, you still have one more test to throw at your overclocked computer; long-term stability. Testing long-term stability is done using a program that causes maximum possible load on all cores for an extended period of time. This causes your processor to draw a high amount of power and create a lot of heat for a long period of time. I usually perform this testing using OCCT.

    To check for long-term stability, you'll want to put the computer under load for a significant period of time. This usually means running the stress test overnight. If your computer can make it through the night without crashing, it is stable. If it crashes, however, then you'll need to back down on the overclock a little and try again. This process is easily the most time-consuming part of overclocking, but by running the stress-test overnight, you can perform it without interrupting normal use of your PC.

    Note that you should keep an eye on system temperature. If you're using OCCT, this will be reported to you. AMD products usually don't like being pushed past 60 degrees Celsius, so if you're seeing a temperature above that, back off your overclock even if the system is stable.

    Once you're able to run a stress test without instability, pat yourself on the back. You've found your maximum overclock. In most instances, your computer will be running 10% to 20% faster than before. Not bad, considering that you didn't have to spend a dime.

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