How to Overclock a CPU

1. Know the precise definition of overclocking and know what you are doing. "Overclocking is the process of forcing a computer component to run at a higher clock rate (the fundamental rate in cycles per second, measured in hertz, at which a computer performs its most basic operations such as adding two numbers or transferring a value from one processor register to another) than designed or designated by the manufacturer".
   
   
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   Understand that not all computers can be overclocked. For one, laptops are pretty much out of the question (some are overheating in stock speed) . Also, any OEM (original equipment manufacturer) computer, such as a Dell, HP or E-machine, will be more difficult to overclock, so your best bet for overclocking is to purchase or build a custom system, but keep in mind that some motherboards can't be used to overclock. Now let's begin.
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   The BIOS Screen
   
   
   
   The BIOS. Overclocking is best done in the computer’s BIOS (Basic Input/Output System or Binary Integrated Operating System). There are also some motherboards that let you do a basic increase in power by setting a jumper, but this is dangerous and you have no real stability control. There are some software programs available which allow you to overclock inside the operating system, but the best results are achieved by changing BIOS settings. Usually you can get into your BIOS by pressing DEL (some systems may use F2, F10, or Ctrl-Enter) as soon as your computer begins the POST (Power On Self Test - when it shows the RAM size, processor speed, etc.). Here, you can change your FSB (front side bus), memory timings, and your CPU multiplier (also referred to as CPU Clock Ratio).
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   Clearing your CMOS. Sometimes, an overclock can become unstable. If this happens, or your computer will not boot, you will need to reset the BIOS back to default and start over again. This is done by clearing the CMOS (a small piece of memory on the motherboard which stores your BIOS configuration, and is powered by a small battery). Some newer motherboards will bypass user settings in the CMOS if the computer fails POST (often caused by a faulty overclock). However, most motherboards require a manual clear. This can be done in two ways, depending on your motherboard. The first way is by changing the position of the clear CMOS jumper on your motherboard, waiting a few minutes, then repositioning the jumper to its original place. Some motherboards have a two-pin clear cmos jumper. In that case, connect the two pins with something metallic, wait a minute or two and disconnect them.
   

   The CMOS Jumper
   The second way, if your motherboard doesn’t have this jumper, consists of unplugging your computer, removing the little CMOS battery, then pressing the power button (your capacitors will discharge), and waiting a couple of minutes. Then you have to refit the battery and plug in your computer. Once your CMOS is cleared, all BIOS settings are reset back to default and you’ll have to start the overclocking process all over again. Just so you know, this step is only necessary if your overclock becomes unstable.
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   Locked or Unlocked. The first thing to know when you start the process of overclocking, is whether your processor is multiplier locked or unlocked. To check whether your CPU is locked, lower your multiplier via the BIOS one step, for example from 11 to 10.5. Save and exit your BIOS and your computer will restart. If your computer posts again and shows the new CPU speed, it means your CPU is unlocked. However, if your computer failed to post (screen remains black) or no CPU speed change is present, this means your multiplier is locked.
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   Multiplier Unlocked Processors. Usually, your max overclock is limited by your memory, or RAM. A good starting place is to find the top memory bus speed in which your memory can handle while keeping it in sync with the FSB. To check this, lower your CPU multiplier some steps (from 11 to 9, for example) and increase your FSB a few notches (e.g.: 200 MHz to 205 MHz). After this, save and exit your BIOS. There are a few ways to test for stability. If you make it into Windows, that is a good start. You can try running a few CPU / RAM intensive programs to stress these components. Some good examples are SiSoft Sandra, Prime95, Orthos, 3DMark 2006 and Folding@Home. You may also choose to run a program outside of Windows, such as Memtest. Load a copy of Memtest onto a bootable floppy, then insert the disk after you have exited the BIOS. Continue to increase your FSB until Memtest starts reporting errors. When this happens, you can try to increase the voltage supplied to your memory. Do note that increasing voltages may shorten the life span of your memory. Also, another option is to loosen the timings on the memory (more on this a bit later). The previous FSB setting before the error will be your max FSB. Your max FSB will fully depend on what memory you have installed. Quality, name-brand memory will work best for overclocking. Now that you know your max FSB, you’ll figure out your max multiplier. Keeping your FSB @ stock, you raise your multiplier one step at a time. Each time you restart, check for system stability. As mentioned above, one good way to do this is by running Prime95. If it doesn’t post (reread the section about clearing the CMOS), or Prime 95 fails, you can try to raise the core voltage a bit. Increasing it may or may not increase stability. On the other hand, the temperature will also be increased. If you are going to increase the core voltage, you should keep an eye on temperatures, at least for a few minutes. Also note that increasing voltages may shorten the life span of your CPU, not to mention void your warranty. When your computer is no longer stable at a given multiplier setting, lower your multiplier one step and take that as your max multiplier. Now that you have your max FSB speed and your max multiplier, you can play around and determine the best settings for your system. Do note that having a higher FSB overclock as opposed to a higher multiplier will have a greater impact on overall system performance.
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   Multiplier Locked Processors. Having a multiplier locked processor means that you can only overclock by increasing the Front Side Bus. We’ll just follow the same strategy as applied in the beginning of the unlocked processors step. Basically, raise the FSB in small increments, and after each post, check the system for stability (Prime95 or Memtest). Also remember that increasing your CPU or RAM voltage can give you more stability. When you reach your peak FSB (probably because of your memory), you can try to get a little further by relaxing your memory timings.
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   Getting Your System Stable. Now that you have an initial overclock, whether with a locked or unlocked processor, you have to tweak the system to get it absolutely stable. This means you have to change the variables (Multiplier, FSB, voltages, memory timings) until the system is rock solid. This is mainly a trial and error process and takes up most of the time when overclocking a system. Here are some thoughts: Your system will start acting strange if your motherboard doesn’t have a PCI /AGP lock. Having a PCI/AGP lock will keep the frequency of your PCI and AGP bus at 33 and 66 MHz respectfully, even if you raise your FSB. Without this lock, the PCI and AGP bus speeds are increased with the FSB, eventually reaching a point where they no longer function correctly. Some motherboards have this lock and some don’t. Check your motherboard / BIOS for such an option. Remember that increasing your voltage will almost always make your system more stable. But as stated before, your temperature will sky rocket and the components lifetime may be decreased. Therefore, the goal is to find the lowest voltage settings at which your system is stable. Decreasing your FSB a few notches may also provide a stable overclock. Sure, you may not want to lower your max overclock, but lowering your FSB 1-2 MHz can mean the difference between a stable system and a BSOD after 25 minutes of gaming. Sometimes, a very high temperature can cause instability as well, so be sure to keep your processor at a decent temperature. One of the ultimate stress tests is Prime 95. When you think your system is stable, run the blend torture test for 12 hours and see if you get any errors. If you don’t, then you should be set. If errors are present, go back to the drawing board. Lower your FSB, increase your voltage, relax your memory timings, etc.
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   Test Utilities. These utilities are designed to put your memory through its paces. If you've got a faulty module or an unstable overclock, these programs will find it. Either one can be loaded onto a floppy disk and used to boot the computer from. They can also be a real life-saver when testing the limits of your hardware. Spare yourself the chance of corrupting a hard drive file system, figure out what works with these first. To use, simply put the program on a floppy disk and boot the computer. The utility will automatically load and begin running the tests. You may find that a CPU overclock that runs either Memtest or WMD successfully without error may not be completely stable in Windows. In these cases, typically a slight increase in CPU voltage will usually resolve the problem. CPU-Z is probably the most popular program to verify and display your system overclock. With the latest version there's even a way to submit your overclock online for verification and to get a comparison link, similar to many graphics benchmarking programs. WCPUID is a similar program, however it has not been updated in some time, and may not recognize all the latest processors and chipsets. Also below are a few Windows-based programs that can help you verify you've got a stable overclock before you actually start using your computer for other tasks. In step 6 it was mentioned that Folding@Home can be used to test stability, however a failure often results in losing the work unit, which is why most people don't like to use F@H for this purpose.
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    Memory Timings. Memory timings or latency refers to how quickly the system can get data in and out of the RAM. This is different from Memory speed, or the frequency that the memory runs at in relation to the processor and system bus. Think of it in terms of a mass-transit system. The memory speed is the rate at which the Metro train moves from station to station. The latency measures how quickly the people can move on and off the train at each stop. Generally, the lower the memory timing value, the less latency there is, and the faster the memory responds. Most BIOS are configured by default to Auto detect timings from the memory module by SPD or Serial Presence Detect, however many have the option to change this to manual so that the user can adjust the settings individually. SPD values are programmed into the memory by the manufacturer, and are typically printed on a label on the side of the module. Timings are usually referred to in this order, along with some available settings in the BIOS.
    

    SPD Values
    CAS is sometimes referred to as CL or Cycle Length. Some motherboards have an option as low as 1.5 for this setting. But the effect of CAS on memory latency is much less than tRCD, tRP or CMD. CMD or Command Rate has the most effect on memory performance. Not all memory and/or motherboards are capable of running a 1T CMD however. Memory manufacturers and overclockers usually refer to memory timings in the same order as listed above. For example, some low-latency memory might indicate CL2 2-2-5 right on a sticker on the module itself. Some memory (such as TCCD) may be rated differently at different speeds such as low timings of 2-2-2-5 at PC3200 (200 Mhz DDR400) and higher timings of 3-4-4-8 at PC4400 (275 Mhz DDR550). Many memory modules do not advertise CMD so you should check reviews before purchasing to get an idea if it will run at 1T.
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    Memory chip quality. There are many manufacturers of individual memory chips (such as Samsung, Winbond, Hynix) and also manufacturers of memory modules (such as Corsair, Kingston, OCZ) who use other companies' chips to make their modules. Memory chips are tested and "binned" by the manufacturer following production and then sold to other companies to make the modules. Some chip manufacturers (such as Samsung, Geil) also make their own modules. Memory chips come in many different flavors so there are a few things to watch for. BH5, or more specifically, Winbond BH-5 chips, have become almost legendary in the overclocking enthusiast world for their ability to run at low latency timings, even at high speeds, albeit when supplied with an extreme amount of voltage. More recently, companies have taken to using BH5-based UTT chips to satisfy overclockers' needs. Some people have had good luck with modules made using these chips, however be aware that the UTT designation means that the chips came untested from the manufacturer. When memory manufacturers have a wafer come off the line that for whatever reason doesn't meet specification, rather than scrap the entire piece they often (depending on market demand) sell off the chips as UTT and it's up to the module manufacturer then to test the chips and determine if they're any good. Since these come out of at least a partially defective wafer, it can't be said with any certainty that the chips can take all the extra voltage and speeds people throw at them. In any case, both UTT and BH5 based modules are typically only good up to ~225 Mhz at the voltages available on most motherboards, i.e.. 2.85 to 2.9 volts. Many DFI motherboards are capable of supplying more than 3 volts to the memory, up to and even including 4 volts! If you don't have a DFI board, you can check out OCZ's DDR Booster to see if it's compatible with your motherboard. For many boards the Booster will give you from 3.4 to 3.8 volts available. The Samsung TCCD is another type of chip that has caught on lately, and may just surpass the BH-5 for "King of the Memory Hill" because it can run at tight timings at default speeds, loose timings at much higher frequencies, and doesn't require much more than stock voltage to keep it running. Most system memory made today is of the TSOP variety, or Thin Small Outline Packages, rather than BGA (more commonly found on video cards) or Ball Grid Array. The names have to do with the way the chips are made and how they attach to the circuit board of the memory module.
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    Athlon 64 Overclocking. Although previous steps of this guide was not processor-specific, the procedures detailed above apply more to Socket A overclocking than the latest A64 chips. There are some significant differences which are worth mentioning to help you get the most out of your Socket 754 or 939 processor. First off, the A64 does not really have a FSB or front side bus speed per se. The term FSB refers to the frequency of the connection between the CPU and Memory Controller. On an Athlon XP chip this could be 133, 166 or 200 (effective 266, 333 or 400 DDR) depending on the model. But the Memory Controller is integrated into the processor on an A64 chip and therefore runs at the same speed as the CPU. There is a connection to the Northbridge on the motherboard however, called the Hypertransport Link, which can be either 800 Mhz (effective 1600) on Socket 754 or 1000 Mhz (effective 2000) on Socket 939. Now the Hypertransport Link speed is determined from the base HTT speed of 200 (referred to as CPU Frequency in this BIOS above) times the HT Multiplier (shown as HT Frequency below) which is by default, 4x on S754 and 5x on S939. It is very important to remember to lower the HT Multi as you increase HTT. Ideally you want to try to keep the overall link speed close to the default 800 or 1000 as going much above these will result in instability. There are cases where someone complains they can't get more than 220-230 HTT on their overclock and think they've topped out the memory or CPU. Had they reduced the HT Multiplier by one step more they likely would have found they could keep going higher on the HTT. Anyway, back to this. The principle behind the CPU Multiplier is the same for A64, only now they refer to it as the FID, or Frequency ID. If you take the base HTT frequency and multiply it by the FID you end up with the speed that the CPU runs at. Unfortunately with A64 processors, only the default multi and lower is unlocked and available to use. Some BIOS will allow half-steps on the FID, however these have been shown to either cause instability or not even work at all, so it's best to just stick with the full multi's. FX chips have all multipliers unlocked, so these can be adjusted both higher or lower than the factory default. Unlike AXP systems, with A64 it is not as important to make sure the FSB remains synchronous with the memory speed. While benchmarks will show a slight increase staying with a 1:1 ratio, going asynchronous is not the detriment to performance it once was. Considering the high speeds available to modern S754 and S939 processors and motherboards, it's a good thing that memory dividers can be implemented. Speaking of memory dividers, this is another setting that sometimes confuses people. While the idea of memory ratios or dividers have existed for a while, AMD users were always told not to use them. Now that we can use them we need to understand that the exact ratio changes slightly depending on the CPU multiplier you use. The reason for this is with the memory controller built into the processor, any divider used takes into account the CPU Multiplier when calculating the ratio. See the chart that shows what the different settings for memory divider in BIOS will result in.
    

    The Different Settings for Memory Divider in BIOS
    The numbers in the top row correspond to the memory speed setting in the BIOS. Some motherboards will only have standard JDEC speeds available such as 200, 166, 133 and 100 whereas others may have the listed "in-between" speeds. The number in parenthesis beside the memory speed indicates the hypothetical ratio for that particular setting. For example, to run memory at 166 we start by taking the base frequency of 200 and multiply that by the ratio of 5/6 and we get 166.66 exactly. However, as mentioned above, the ratio has to be a factor of the CPU Multiplier, so we need to look at the row indicated by the multiplier being used. For example, a 3000+ "Venice" stock multi is 9x, so if you come down to that row, then move across the row to the 166 memory column you find that the ratio used for this setting will actually be 9/11 rather than the 5/6 as indicated at the top. The 9/11 ratio yields a memory speed of 163.63 which is close, but not quite the same as what it should be for a true 166 speed. This is not a problem but just something to be aware of.