What is Overclocking?
Overclocking is the process of making various components of your computer run at faster speeds than they do when you first buy them. For instance, if you buy a Pentium 4 3.2GHz processor, and you want it to run faster, you could overclock the processor to make it run at 3.6GHz.
Why would you want to overclock? Well, the most obvious reason is that you can get more out of a processor than what you payed for. You can buy a relatively cheap processor and overclock it to run at the speed of a much more expensive processor. If you're willing to put in the time and effort, overclocking can save you a bunch of money in the future or, if you need to be at the bleeding edge like me, can give you a faster processor than you could possibly buy from a store
The Dangers of Overclocking
First of all, let me say that if you are careful and know what you are doing, it will be very hard for you to do any permanent damage to your computer by overclocking. Your computer will either crash or just refuse to boot if you are pushing the system too far. It's very hard to fry your system by just pushing it to it's limits.
There are dangers, however. The first and most common danger is heat. When you make a component of your computer do more work than it used to, it's going to generate more heat. If you don't have sufficient cooling, your system can and will overheat. By itself, overheating cannot kill your computer, though. The only way that you will kill your computer by overheating is if you repeatedly try to run the system at temperatures higher than recommended. As I said, you should try to stay under 60 C.
Don't get overly worried about overheating issues, though. You will see signs before your system gets fried. Random crashes are the most common sign. Overheating is also easily prevented with the use of thermal sensors which can tell you how hot your system is running. If you see a temperature that you think is too high, either run the system at a lower speed or get some better cooling. I will go over cooling later in this guide.
The other "danger" of overclocking is that it can reduce the lifespan of your components. When you run more voltage through a component, it's lifespan decreases. A small boost won't have much of an affect, but if you plan on using a large overclock, you will want to be aware of the decrease in lifespan. This is not usually an issue, however, since anybody that is overclocking likely will not be using the same components for more than 4-5 years, and it is unlikely that any of your components will fail before 4-5 years regardless of how much voltage you run through it. Most processors are designed to last for up to 10 years, so losing a few of those years is usually worth the increase in performance in the mind of an overclocker.
To understand how to overclock your system, you must first understand how your system works. The most common component to overclock is your processor.
When you buy a processor, or CPU, you will see it's operating speed. For instance, a Pentium 4 3.2GHz CPU runs at 3.2GHz, or 3200 MHz. This is a measurement of how many clock cycles the processor goes through in one second. A clock cycle is a period of time in which a processor can carry out a given amount of instructions. So, logically, the more clock cycles a processor can execute in one second, the faster it can process information and the faster your system will run. One MHz is one million clock cycles per second, so a 3.2GHz processor can go through 3,200,000,000, or 3 billion two hundred million clock cycles in every second. Pretty amazing, right?
The goal of overclocking is to raise the GHz rating of your processor so that it can go through more clock cycles every second. The formula for the speed of your processor if this:
FSB (in MHz) x Multiplier=Speed in MHz.
Now to explain what the FSB and Multiplier are:
The FSB (or, for AMD processors, the HTT*), or Front Side Bus, is the channel through which your entire system communicates with your CPU. So, obviously, the faster your FSB can run, the faster your entire system can run.
CPU manufacturers have found ways to increase the effective speed of the FSB of a CPU. They simply send more instructions in every clock cycle. So instead of sending one instruction every one clock cycle, CPU manufacturers have found ways to send two instructions per clock cycle (AMD CPUs) or even four instructions per clock cycle (Intel CPUs). So, when you look at a CPU and see it's FSB speed, you must realize that it is not really running at that speed. Intel CPUs are "quad pumped", meaning they send 4 instructions per clock cycle. This means that if you see an FSB of 800MHz, the underlying FSB speed is really only 200MHz, but it is sending 4 instructions per clock cycle so it achieves an effective speed of 800MHz. The same logic can be applied to AMD CPUs, but they are only "double pumped", meaning they only send 2 instructions per clock cycle. So an FSB of 400MHz on an AMD CPU is comprised of an underlying 200MHz FSB sending 2 instructions per clock cycle.
This is important because when you are overclocking, you will be dealing with the real FSB speed of the CPU, not the effective CPU speed.
The multiplier portion of the speed equation is nothing more than a number that, when multiplied by the FSB speed, will give you the total speed of the processor. For instance, if you have a CPU that has a 200MHz FSB (real FSB speed, before it is double or quad pumped) and has a multiplier of 10, then the equation becomes:
(FSB) 200MHz x (Multiplier) 10= 2000MHz CPU speed, or 2.0GHz.
On some CPUs, such as the Intel processors since 1998, the multiplier is locked and cannot be changed. On others, such as the AMD Athlon 64 processors, the multiplier is "top locked", which means that you can change the multiplier to a lower number but cannot raise it higher than it was originally. On other CPUs, the multiplier is completely unlocked, meaning you can change it to any number that you wish. This type of CPU is an overclockers dream, since you can overclock the CPU simply by raising the multiplier, but is very uncommon nowadays.
It is much easier to raise or lower the multiplier on a CPU than the FSB. This is because, unlike the FSB, the multiplier only effects the CPU speed. When you change the FSB, you are really changing the speed at which every single component of your computer communicates with your CPU. This, in effect, is overclocking all of the other components of your system. This can bring about all sorts of problems when other components that you don't intend to overclock are pushed too far and fail to work. Once you understand how overclocking works, though, you will know how to prevent these issues.
*On AMD Athlon 64 CPUs, the term FSB is really a misnomer. There is no FSB, per se. The FSB is integrated into the chip. This allows the FSB to communicate with the CPU much faster than Intel's standard FSB method. It also can cause some confusion, since the FSB on an Athlon 64 can sometimes be referred to as the HTT. If you see somebody talking about raising the HTT on an Athlon 64 CPU and is talking about speeds that you recognize as common FSB speeds, then just think of the HTT as the FSB. For the most part, they function in the same way and can be treated the same and thinking of the HTT as the FSB can eliminate some possible confusion.
How to Overclock
So now you understand how a processor gets it's speed rating. Great, but how do you raise that speed?
Well, the most common method of overclocking is through the BIOS. The BIOS can be reached by pressing a variety of keys while your system is booting up. The most common key to get into the BIOS is the Delete key, but others may be used such as F1, F2, any other F button, Enter, and some others. Before your system starts loading Windows (or whatever OS you have), it should have a screen that will tell you what button to use at the bottom.
Once you are in the BIOS, assuming that you have a BIOS that supports overclocking*, you should have access to all of the settings needed to overclock your system. The settings that you will most likely be adjusting are:
Multiplier, FSB, RAM Timings, RAM Speed, and RAM Ratio.
On a very basic level, all you are trying to do is to get the highest FSB x Multiplier formula that you can achieve. The easiest way to do this is to just raise the multiplier, but that will not work on most processors since the multiplier is locked. The next method is to simply raise the FSB. This is pretty self explanatory, and all of the RAM issues that have to be dealt with when raising the FSB will be explained below. Once you've found the speed at which the CPU won't go any faster, you have one more option.
If you really want to push your system to the limit, you can try lowering the multiplier in order to raise the FSB even higher. In order to understand this, imagine that you have a 2.0GHz processor that has a 200MHz FSB and a 10x multiplier. So 200MHz x 10=2.0GHz. Obviously, that equation works, but there are other ways to get to 2.0GHz. You could raise the multiplier to 20 and lower the FSB to 100MHz, or you could raise the FSB to 250MHz and lower the multiplier to 8. Both of those combinations would give you the same 2.0GHz that you started out with. So both of those combinations should give you the same system performance, right?
Wrong. Since the FSB is the channel through which your system communicates with your processor, you want it to be as high as possible. So if you lowered the FSB to 100MHz and raised the multiplier to 20, you would still have a clock speed of 2.0GHz, but the rest of the system would be communicating with your processor much slower than before resulting in a loss in system performance.
Ideally, you would want to lower the multiplier in order to raise the FSB as high as possible. In principle, this sounds easy, but it gets complicated when you involve the rest of the system, since the rest of the system is dependent on the FSB as well, chiefly the RAM. Which leads me to the next section on RAM.
*Most retail computer manufacturers use motherboards and BIOSes that do not support overclocking. You won't be able to access the settings you need from the BIOS. There are utilities that will allow you to overclock from your desktop, but I don't recommend them since I have never tried them out myself.
RAM and what it has to do with Overclocking
As I said before, the FSB is the pathway through which your system communicates with your CPU. So raising the FSB, in effect, overclocks the rest of your system as well.
The component that is most affected by raising the FSB is your RAM. When you buy RAM, it is rated at a certain speed. I'll use the table from my post to show these speeds:
PC-2100 - DDR266
PC-2700 - DDR333
PC-3200 - DDR400
PC-3500 - DDR434
PC-3700 - DDR464
PC-4000 - DDR500
PC-4200 - DDR525
PC-4400 - DDR550
PC-4800 - DDR600
Note how the RAM's rated speed is DDR PC-4000. Then refer to this table and see how PC-4000 is equivalent to DDR 500.
To understand this, you must first understand how RAM works. RAM, or Random Access Memory, serves as temporary storage of files that the CPU needs to access quickly. For instance, when you load a level in a game, your CPU will load the level into RAM so that it can access the information quickly whenever it needs to, instead of loading the information from the relatively slow hard drive.
The important thing to know is that RAM functions at a certain speed, which is much lower than the CPU speed. Most RAM today runs at speeds between 133MHz and 300MHz. This may confuse you, since those speeds are not listed on my chart.
This is because RAM manufacturers, much like the CPU manufacturers from before, have managed to get RAM to send information twice every RAM clock cycle.* This is the reason for the "DDR" in the RAM speed rating. It stands for Double Data Rate. So DDR 400 means that the RAM operates at an effective speed of 400MHz, with the "400" in DDR 400 standing for the clock speed. Since it is sending instructions twice per clock cycle, that means it's real operating frequency is 200MHz. This works much like AMD's "double pumping" of the FSB.
So go back to the RAM that I linked before. It is listed at a speed of DDR PC-4000. PC-4000 is equivalent to DDR 500, which means that PC-4000 RAM has an effective speed of 500MHz with an underlying 250MHz clock speed.
So what does this all have to do with overclocking?
Well, as I said before, when you raise the FSB, you effectively overclock everything else in your system. This applies to RAM too. RAM that is rated at PC-3200 (DDR 400) is rated to run at speeds up to 200MHz. For a non-overclocker, this is fine, since your FSB won't be over 200MHz anyway.
Problems can occur, though, when you want to raise your FSB to speeds over 200MHz. Since the RAM is only rated to run at speeds up to 200MHz, raising your FSB higher than 200MHz can cause your system to crash. How do you solve this? There are three solutions: using a FSB:RAM ratio, overclocking your RAM, or simply buying RAM rated at a higher speed.
Since you probably only understood the last of those three options, I'll explain them:
FSB:RAM Ratio: If you want to raise your FSB to a higher speed than your RAM supports, you have the option of running your RAM at a lower speed than your FSB. This is done using an FSB:RAM ratio. Basically, the FSB:RAM ratio allows you to select numbers that set up a ratio between your FSB and RAM speeds. So, say you are using the PC-3200 (DDR 400) RAM that I mentioned before which runs at 200MHz. But you want to raise your FSB to 250MHz to overclock your CPU. Obviously, your RAM will not appreciate the raised FSB speed and will most likely cause your system to crash. To solve this, you can set up a 5:4 FSB:RAM ratio. Basically, this ratio will mean that for every 5MHz that your FSB runs at, your RAM will only run at 4MHz.
To make it easier, convert the 5:4 ratio to a 100:80 ratio. So for every 100MHz your FSB runs at, your RAM will only run at 80MHz. Basically, this means that your RAM will only run at 80% of your FSB speed. So with your 250MHz target FSB, running in a 5:4 FSB:RAM ratio, your RAM will be running at 200MHz, which is 80% of 250MHz. This is perfect, since your RAM is rated for 200MHz.
This solution, however, isn't ideal. Running the FSB and RAM with a ratio causes gaps in between the time that the FSB can communicate with the RAM. This causes slowdowns that wouldn't be there if the RAM and the FSB were running at the same speed. If you want the most speed out of your system, using an FSB:RAM ratio wouldn't be the best solution.
Overclocking your RAM
Overclocking your RAM is really very simple. The principle behind overclocking RAM is the same as overclocking your CPU: to get the RAM to run at a higher speed than it is supposed to run at. Luckily, the similarities between the two types of overclocking end there, or else RAM overclocking would be much more complicated than it is
To overclock RAM, you just enter the BIOS and attempt to run the RAM at a higher speed than it is rated at. For instance, you could try to run PC-3200 (DDR 400) RAM at a speed of 210MHz, which would be 10MHz over the rated speed. This could work, but in some cases it will cause the system to crash. If this happens, don't panic. The problem can be solved pretty easily by raising the voltage to your RAM. The voltage to your RAM, also known as vdimm, can be adjusted in most BIOSes. Raise it using the smallest increments available and test each setting to see if it works. Once you find a setting that works, you can either keep it or try to push your RAM farther. If you give the RAM too much voltage, however, it could get fried.
The only other thing that you have to worry about when overclocking RAM are the latency timings. These timings are the delays between certain RAM functions. If you want to raise the speed of your RAM, you may have to raise the timings. It's not all that complicated, though, and shouldn't be too hard to understand.
That's really all there is to it. If only overclocking the CPU were that easy
Buying RAM rated at a Higher Speed
This one's the simplest thing in this entire guide If you want to raise your FSB to, say, 250MHz, just buy RAM that is rated to run at 250MHz, which would be DDR 500. The only downside to this option is that faster RAM will cost you more than slower RAM. Since overclocking your RAM is relatively simple, you might want to consider buying slower RAM and overclocking it to fit your needs. It could save you over a hundred bucks, depending on what type of RAM you need.
That's basically all you need to know about RAM and overclocking. Now onto the rest of the guide.
Voltage and how it affects Overclocking
There will be a point when you are overclocking and you simply cannot increase the speed of your CPU anymore no matter what you do and how much cooling you have. This is most likely because your CPU is not getting enough voltage. This is very similar to the RAM voltage scenario that I addressed above. To solve this, you simply up the voltage to your CPU, also known as the vcore. Do this in the same fashion described in the RAM section. Once you have enough voltage for the CPU to be stable, you can either keep the CPU at that speed or attempt to overclock it even further. As with the RAM, be careful not to overload the CPU with voltage. Each processor has recommended voltages setup by the manufacturer. Look on the website to find these. Try not to go past the recommended voltages.
Keep in mind that upping the voltage to your CPU will cause much greater heat output. This is why it is essential to have good cooling when overclocking. Which leads me to my next topic...
As I said before, when you up the voltage to your CPU, the heat output great increases. This makes proper cooling a necessity.
There are basically three "levels" of case cooling:
Air Cooling (Fans)
Peltier/Phase Change Cooling (VERY expensive and high end cooling[/b]
I really don't have much knowledge on the Peltier/Phase Change method of cooling, so I won't address it. All you need to know is that it could cost you upwards of $1000 dollars and can keep your CPU at sub-zero temperatures. It's intended for VERY high end overclockers, and I assume that nobody here will be using it.
The other two, however, are much more affordable and realistic.
How hot is too hot/How much voltage is too much?
As a general guideline for safe temperatures, temps at full load should be at or below 60C for a P4 and 55C for Athlons. Lower is better, but don't freak if your temps are high. Check the resource, and see if it is well within specifications (as it likely is). For voltages, 1.65-1.7 is a good limit for a P4 and an Athlon can go up to 1.8 on air/2.0 on water - generally speaking. Depending on cooling, more voltage/less voltage may be appropriate. The limits on chips are surprisingly high. For example, the maximum temperature/voltage on a Barton core Athlon XP+ is 85C and 2.0 volts. 2 volts is plenty for most overclocks, and 85C is rather high.
Do I need better cooling?
Depends on what your current temperatures are and what you're planning to do with your system. If your temperatures are too high, then you probably need better cooling, or at least need to reseat your heatsink and work on cable management. Good cable management can do wonders for case airflow. Also, proper application of thermal paste is very important for temps. Use the guide from the TIM(Thermal Interface Material) manufacturer and follow it as closely as you can. If that doesn't help enough or at all, than you probably need better cooling. But see the above section and included link before you start complaining about your temperatures. We don't really want to hear it, unless they are spectacularly bad (or good). Then again, most of those instances can be chalked up to inaccurate temperature sensors on the motherboard. So don't post these questions unless you really can't figure it out and you have tried a few things already.
What are the common methods of cooling?
The most common method is air cooling. This involves putting a fan on top of a heatsink which is then placed on top of the CPU. These can be either very quiet, very loud, or somewhere in between, based on the fan used. They can be fairly effective coolers, but there are more effective cooling solutions. One of these is watercooling, but I'll get into that in a bit.
Air coolers are made by companies such as Zalman, Thermalright, Thermaltake, Swiftech, Alpha, Coolermaster, Vantec, etc. Zalman makes some of the best quiet cooling units and is known for their "flower cooler" design. They have one of the most effective quiet cooling designs in the 7000Cu/AlCu (all copper or aluminum and copper construction) and it is also one of the better performing designs. Thermalright is (quite) arguably the producer of the highest performing heatsinks when used with appropriate fans. Swiftech and Alpha were the performance kings before Thermalright came into the spotlight and are still excellent heatsinks and can be used in more applications than the Thermalright heatsinks because they are generally smaller than the Thermalright heatsinks and so fit on more motherboards. Thermaltake produces an abundance of cheap heatsinks, but they aren't really worth it IMHO. They don't perform on the same level as the other heatsink manufacturers' heatsinks, but they can be used in a pinch or in a budget box. That covers the most popular heatsink manufacturers.
On to watercooling. Watercooling is still mainly a fringe movement, but it is becoming more mainstream all the time. NEC and HP (I believe) make watercooled systems that can be bought retail. Still, most of watercooling is in the enthusiast area. There are several components involved in a watercooling loop, even the most basic one. There is at least one waterblock, usually on the CPU and sometimes the GPU. There is a pump and sometimes a reservoir. There is also a radiator or two.
The waterblocks are generally constructed from copper or (less commonly) aluminum. Even less common, but becoming more so, is waterblocks made of silver. Danger Den makes the S-TDX, and it is possible to procure a silver Cascade block. There are several different kinds of internal designs for waterblocks, but I won't get into those here. Visit the watercooling sub forum to learn more. The pump is responsible for pushing water through the loop. The most common pumps are Eheim pumps (1046, 1048, 1250), Hydor (L20/L30), and the Danner Mag3. Iwaki pumps are also popular among the high-end crowd. The Swiftech MCP600 pump is becoming more popular, as is the Liang D4. Both of those are high-head 12V pumps. A reservoir is helpful because it adds to the volume of the water in the loop and makes filling and bleeding (getting the air bubbles out of the loop) and maintenance easier. However, it takes up a good deal of space in most cases (a small reservoir isn't much good) and it is just one more thing that could leak. The radiator can either be a retail one, such as Swiftech's radiators or the Black Ice radiators, or made from a heatercore from a car. The heatercores generally offer superior performance as well as a lower price tag, but are also harder to assemble, as they usually don't come in a form that can be adopted to watercooling quickly or easily. Oil coolers are an alternative for those with strange size requirements, as they come in a great variety of shapes and sizes (well, usually a rectangle). However, they don't perform quite as well as a heatercore. Again, look at the watercooling sub forum for more info. The tubing is also a factor in performance. Generally, 1/2" ID is considered to be the best for high performance. However, 3/8" and even 1/4" ID setups are becoming more common, and their performance is also getting closer to that of a 1/2" ID loop. That's about it for watercooling in this section.
What are some of the less common cooling types?
Phase change, chilled water, peltier (TEC), and submersion setups are less common, but higher performance, cooling alternatives to those listed above. Ask in the extreme cooling sub forum about any of these methods. Read up on any of these before you use them. Peltier cooling and chilled water loops are both based on watercooling, in that they are based on a modified watercooling loop. Peltier is the most common of these types. A peltier is a device that, when current is applied, gets hot on one side and cold on the other. This can be used between a CPU and a waterblock or a GPU and a waterblock. Less common is peltier cooled northbridges, but this isn't really necessary. Ever. A chilled water loop uses either a peltier or phase change to cool off the water in the loop, usually replacing the radiator in the loop cooling the CPU/GPU. Using a peltier to do this is not very effective, because it often requires another watercooling loop to cool it off. The peltier is generally sandwiched between either a heatsink and a waterblock or a waterblock and another waterblock. The phase change method involves placing the cooling head or cooling component from an A/C unit or the like in a reservoir. Antifreeze is usually added to the water in about a 50/50 ratio in chilled water setups, because freezing isn't good. The tubing has to be insulated as do the blocks if sub ambient temperatures are ever reached in case of condensation. Phase change involves a compressor and a cooling head attached to the CPU or sometimes the GPU. I won't go into much depth about it here. Read up on it at overclockers.com or the extreme cooling sub forum or your extreme overclocking forum of choice.
Other less common methods involve dry ice, liquid nitrogen, watercooling the PSU and hard drives, and other things like that. Using the case as a heatsink has also been considered and done as well.
I just thought up a cool idea for cooling, is it original?
Is it listed up above? If so, then no. Also, the search function is a wonderful thing now that it works.
My cool idea has been listed already, should I post it?
Only if you are in the process of doing it. Then we want - no, demand - pictures. Hypothetical discussions are okay, but make sure it is something useful. Don't let me discourage you though, just don't take it too hard if no one cares.
What about prebuilt watercooling units?
The Koolance one and the Corsair one are the only ones really worth considering. The little Globalwin one is alright, but no better than any half-decent air cooling. The rest are no better. Avoid them. The newest Thermaltake one may be alright, but see the above warning about Thermaltake products. New kits may be decent (The kingwin one seems to be so) but read multiple reviews and at least one that tests it on the platform you will be using before buying anything.
What are the dangers of overclocking?
There are several dangers attached to overclocking, and they should definitely not be overlooked. Running any component out of spec will shorten its lifespan; though newer chips are able to deal with this far better than older ones, so this is less of a problem than it used to be, especially if you upgrade every 6 months or every year. For long term stability, IE computers that are going to be running for more than 2 years or so with a load most of the time, overclocking is not a good idea. Also, there is the possibility that overclocking will corrupt data, so if you don't do backups of any data you care about, overclocking is not really for you (and you should really start doing backups anyway) unless you can easily replicate the data and it will not cause any problems. But take possible data loss into account BEFORE you start overclocking. You will thank yourself for doing this if anything goes wrong. Overclocking (especially large overclocks at a high voltage) is not recommended if you only have one computer and you need it for anything important, as the possibility of component failure is quite real (I have lost a few components to overclocking, but not as many as some have lost) so that needs to be taken into account as well. On a lighter note, addiction and "Empty Wallet Syndrome" are also very real risks to overclocking.
How do I overclock?
This is a rather complex question, but the basics are pretty easy. The simplest method is to just raise the FSB. This will work on almost any platform. However, Via chipsets (KT266/333/400(a)/600/880(the 880 may have a lock, but I think it still lacks one) and K8T800 - not to be confused with the K8T800 Pro which has one) do not have a PCI/AGP lock, so you have to be careful about raising the FSB, as running the PCI bus out of spec (33mhz is the standard speed) can corrupt hard drive data, prevent peripherals from functioning correctly (especially ATI AGP video cards), and generally cause instability. This will be revisited later. The nForce2 chipset for AMD's XP chip, the nForce3 250 (the 150 is unlocked on most boards, but some motherboards have either dividers or rudimentary locks to allow higher FSB, but I'm not an expert on these - ask around), the Via K8T800 Pro, and the Intel 865/875 chipsets all possess locked PCI frequencies. Many, if not all, i845 based motherboards also have the PCI/AGP lock. This makes adjusting the FSB far easier, as it removes certain limiting factors, such as frequency-sensitive peripherals (most of them). However, limits still exist. Besides the limit imposed by the chip itself, the RAM and the chipset, as well as the motherboard itself, can limit the FSB that can be attained. That is where multiplier adjustment comes in.
On certain Athlon XP chips, the multiplier is adjustable. These chips are referred to as 'unlocked.' The Athlon 64 series (I believe) allows multiplier adjustment to lower multipliers only aside from the fully unlocked FX series. The Pentium 4 is locked unless you have acquired an engineering sample through some stroke of luck or ebay. However, almost all motherboards allow multiplier adjustment as long as the chip supports it. For the Athlon XP boards that don't, a pinmodding guide to raise/lower the multiplier is available in the 'workshop' section of ocinside.de/index_e.html
. The site explains how to perform the modification and also has several other useful tools.
Once the system becomes unstable because of the CPU limitations, there are two options. You can either back down a little to where it is stable, or you can raise the CPU voltage (and possibly the RAM and AGP voltages) to where it becomes stable, or even raise it higher and keep pushing the overclock. You can also try 'loosening' the memory timings (raising the numbers) until it becomes stable if raising the CPU voltage doesn't help or raising the memory voltage. If none of these help, your motherboard may have a provision for raising the chipset voltage, which can help if your chipset is adequately cooled. If nothing helps, you may need better cooling on the CPU or other components (cooling the MOSFETS - the little chips next to the CPU socket which regulate power - can help and is rather common) If that still doesn't help, or the gain is only marginal, you are at the limit of your chip or your motherboard. If lowering the voltage doesn't hurt stability than it is most likely your motherboard. Voltmodding the chipset is a possibility, but is a bit advanced and requires better cooling than stock. Also, cooling the southbridge as well as the northbridge may help, or may improve stability. I know that on my motherboard, the integrated sound starts to crackle if I run WinAMP/XMMS and UT2004 (this happens in both Windows and Linux) no matter the FSB if i don't have a heatsink on the southbridge. So it isn't a bad idea, but may not be necessary. It also generally voids your warranty (more than overclocking does - overclocking can usually be undone without a trace).
That covers basic overclocking. More advanced overclocking usually involves adding heatsinks to everything, voltmodding the motherboard and possibly power supply, adding more/better fans and/or watercooling and/or phase change/cascade cooling. Google can help you learn about the more extreme side of overclocking.
What do I do if my computer won't post (Display the BIOS screen when it is turned on)?
This varies based on the motherboard you have. The "fail-safe" solution (unless you killed something) is to reset the CMOS, usually by moving a jumper for a set amount of time. Check your motherboard manual for the specifics. Most recent enthusiast level boards have an option to post at reduced frequencies if the overclock is pushed too high but leave the BIOS settings intact, so you can go in and lower the clock speed to where it is stable. On some motherboards, this is done by holding the Insert key when you turn on the computer (usually has to be a PS/2 keyboard). The DFI LanParty PRO875 is one such board. Others automatically reduce the frequency if the computer didn't post on the previous attempt. The A7N8X usually does this. Sometimes a computer will not cold boot (post when the power button is pressed) but will work if it is left on for a while, then reset. On other occasions the computer will cold boot fine, but will fail to warm boot (reboot). Those are both indications of instability, but if you are happy with the stability and able to deal with the issues than it usually won't cause any huge problems.
What limits my overclock?
Generally, the RAM and CPU are the only significant limiting factors, especially in AMD systems because of the problems inherent in running the memory asynchronously (see the FSB section down below) The RAM has to run at the same speed as the FSB or at a fraction of it. Complex fractions are allowed, meaning the memory can be run at a higher rate than the FSB, not just a lower one. With the option to run looser timings/more voltage through memory, though, it is becoming less and less the limiting factor, especially since newer platforms (P4 and A64) suffer less of a performance hit from running async. (again, see below) The CPU has become the main limiting factor. The only way to deal with a CPU that doesn't want to run any faster is to pump more voltage through it, though exceeding the maximum core voltage shortens the life of the chip (though overclocking does this as well) but sufficient cooling stems this problem. Another problem with running too high of a core voltage manifested itself on the P4 platform in the form of SNDS, or Sudden Northwood Death Syndrome, wherein running any voltage over something like 1.7 (not sure of the exact number, no one is) would result in the quick and untimely death of the processor, even with phase change cooling. However, the newer 'C' core chips, the EE chips, and the Prescott chips have not had this problem, at least not to nearly the same extent. The cooling can also prevent a good overclock, as having temps that are too high can lead to instability. But if your system is stable, then the temps usually are not too high.
Now that I've overclocked a lot, what should I do?
Run some benchmarks if you want to. Run Prime95 (Or your stress test of choice - it is up to you) for a sufficient time period (Usually 24 hours straight is considered a stable system)
/Begin shameless F@H plug
Then install Folding@Home if you haven't already.
/End shameless F@H plug
That covers the basic aspects of overclocking. The questions from this point on are the more technically involved sections.
What is the FSB?
FSB (or the Front Side Bus) is one of the easiest and most common ways to overclock. The FSB is the speed at which the CPU interfaces with the rest of the system. It also affects the memory clock, which is the speed the memory runs at. Generally speaking, higher=better for both the FSB and the memory clock. However, there are certain cases where this is not true. For example, running the memory clock faster than the FSB does not really help at all. Also, on Athlon XP systems, running the FSB at a higher rate, but forcing the memory to run out of sync with the FSB (using memory dividers which will be discussed later on) will hamper performance far more than running at a lower FSB with the memory in sync.
The FSB is referred to in different ways on Athlon and P4 systems. On the Athlon side, it is a DDR bus, meaning that if the actual clock is 200mhz, it is said to be running at 400mhz. On a P4, it is "Quad-Pumped" so if the actual clock is the same 200mhz, it is said to be 800mhz. This makes for a good marketing strategy for Intel, because as every average Joe knows, higher=better. Intel's "Quad-Pumped" FSB actually has a real-world advantage, as it is what allows P4 chips to run the memory out of sync with less performance loss. The higher rate of cycles per clock gives it a better chance of having the memory cycles line up with the CPU cycles, which equates to better performance.
Why does running the PCI/AGP bus out of spec cause instability?
Running the PCI bus out of spec causes instability mainly because it forces components with very strict tolerances to run at a different frequency then they are intended to. The PCI spec is usually stated at 33mhz. Sometimes it is stated at 33.3mhz, which I believe is closer to the real spec. The main victim of high PCI speeds is the hard drive controller. Certain controller cards have a higher tolerance than others, and so are able to run at increased speeds without noticeable corruption. However, the onboard controllers on most motherboards (especially SATA controllers) are extremely sensitive to high PCI speeds, and can have corruption and data loss if the PCI bus is running at even 35mhz. Most are able to do 34mhz, as it is really less then 1mhz out of spec (depending on where the motherboard stops rounding to 34mhz... for example, most motherboards will probably report any FSB from 134mhz-137 as being a 34mhz PCI speed. The actual range is from 33.5mhz to 34.25mhz, and may vary even more based on variations in the clock frequency of the motherboard. At higher FSBs and higher dividers, the range can be even more). Audio and other integrated peripherals also suffer when the PCI bus is run out of spec. ATI video cards are a lot less tolerant to high AGP speeds (directly related to PCI speed) than nVidia cards. With that in mind, most Realtek lan cards (the PCI based ones that occupy an expansion slot) are rated for safe operation at anywhere from 30-40mhz.
What is the multiplier?
The multiplier acts in conjunction with the FSB to determine the clock speed of the chip. For example, a multiplier of 12 with a FSB of 200 will give a clock speed of 2400mhz. As explained in the overclocking section above, some chips are locked and some are unlocked, meaning only certain chips allow adjustment of the multiplier. If you have multiplier adjustment, it can be used to either get a higher clock speed if the FSB is limited on your motherboard or to allow a higher FSB if the chip is limited.
What is a memory divider?
A memory divider determines the ratio of the memory clock speed to the FSB. A 2:1 FSB:RAM divider would net a 100mhz ram clock with an FSB of 200mhz. The most common use of a divider is to allow a P4C system to run 250FSB with PC3200 ram, with a 5:4 divider. There are also 4:3 dividers and 3:2 dividers on most Intel (DDR1) systems. Athlon systems can't use the memory as efficiently as P4 systems when a divider is used, as explained above in the FSB section. The memory dividers should only be used to obtain stability, not just at a whim, because even on a P4 it hurts performance somewhat. If your system is stable without resorting to a memory divider (or if a memory voltage bump can fix the problem) then don't use the dividers.
What do the different memory timings mean?
CAS Latency , sometimes referred to as CL or CAS, is the minimum number of cycles the ram must wait until it can read or write again. Obviously, the lower the number (time), the better.
tRCD is the delay before the data on a particular row in memory is read/written. Again, the lower the number the better.
tRP is basically the precharge time of the row. tRP is the time the system waits after writing something to a row before another row can be active. Once again, lower is better.
tRAS is the minimum value for how long a row can be active. So basically, tRAS is how long the row has to be turned on. This number varies quite a bit with RAM settings.
What do the various memory ratings refer to? (PC2100/PC2700/PC3200 etc.)
The rating refers directly to the maximum bandwidth obtainable and indirectly to the memory clock rate. PC2100, for example, has a 2.1GB/S maximum transfer rate, and a clock rate of 133mhz. PC4000, as another example, has a 4GB/S ideal transfer rate and a 250mhz clock. To obtain the clock rate from the PCXXXX rating, divide the rating by 16. Multiply the mhz rating by 16 to obtain the bandwidth rating.
How does the DDRXXX refer to the actual clock speed of the memory?
The DDRXXX is just two times the actual clock speed; i.e. DDR400 is clocked at 200mhz.
if you want know the pc-XXXX speed of the DDRXXX speed, times it by 8.