Firstly, Overclocking is the practice of running your CPU (or other components) past the speed they are rated at. The basics are not as difficult as you may think although due care and patience should be taken at all times and any oc'ing should be done incrementally.
Intel and AMD manufacture their CPUs and then test them at a certain speed. If the CPU fails at a certain speed, then it is sold as a CPU at the next lower speed. The tests are very stringent so a CPU may be able to run at the higher speed reliably. In fact, the tests are often not used at all. For example, once a company has been producing a certain CPU for a while, they have gotten the process down well enough that all the CPUs they make will run reliably at the highest speed the CPU is designed for. So just to reach market demand, they will mark some of them as the slower CPUs.
I've got to put a disclaimer here though: You do this at your own risk, I'm not advocating you do it, just that it can be done. Rule of thumb: DON'T o.c any component you can't afford to replace as o.c'ing can ruin your whole computer.
Again though, if you're careful and take your time and with all the built in safeguards resident within a pc it is unlikely that you will permanently damage a component. More often than not your pc will just crash or refuse to boot.
Overclocking can give you a level of performance of higher priced pc components therefore saving you money.
There are other concerns though. The most common is one of heat. When you make a pc component run faster or up it's voltage 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. With a Core2 (which i believe you have) try to stay below 50c at peak. I'd recommend purchasing/downloading some thermal measuring software and/or purchasing heat sensors. Some mobo manufacturers include such things with the mobo.
Don't be too worried about overheating though. You'll see the signs before your system gets fried. Random crashes are the most common sign.
Another dange of oc'ing is that it can reduce the lifespan of your components. When you run more voltage through a component, its lifespan decreases. A small increase won't have much of an affect, but if you plan on using a high overclock, you will want to be aware of the decrease in lifespan. This isn't 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.
To understand how to overclock your system, you must first understand how your system works. The first component people o.c usually is the cpu:
When you purchase a CPU, you will see its operating speed. A Core2 E6400 runs at 2.13ghz or 2130mhz. This is a measure 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, (the more clock cycles a processor can execute in one second, the faster it can process information and the faster your system will run).
The aim of overclocking is to increase the GHz rating of your processor so that it can go through more clock cycles per 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 Front Side Bus, is how your entire system communicates with your CPU. 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 by sending more instructions in each clock cycle. So instead of sending one instruction every one clock cycle, Intel send's 4 instructions per clock cycle. So, when you look at your fsb and see its speed of 1066mhz, it isn't really running at that speed. Intel's CPUs are "quad pumped". This means that the fsb on your core2 is really running at 266mhz. What you see is the effective speed when taking into account the quad-pumped measure
I mention this because when you're o.c'ing you're dealing with the actual fsb not the effective.
The multiplier part of the speed equation is purely 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 266MHz FSB (actual FSB speed) and has a multiplier of 8, then the equation becomes:
(FSB) 266MHz x (Multiplier) 8 = 2133MHZ for the cpu, or 2.13GHZ
(I realise these equations don't total exactly but i'm using the manufacturer's ranges to keep things simple and a hertz here or there makes no difference)
On the majority of CPU's the multiplier is locked and cannot be raised but can be reduced. This is known as top-locking.
On some CPU's however, the multiplier is completely unlocked ( Eg: X6800), meaning you can change it to any number that you want. This type of CPU is an overclocker's favourite, as it means you can overclock the CPU simply by raising the multiplier.
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 affects the CPU speed. When you change the FSB, you are 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 cause 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.
The most common method of overclocking is through the BIOS. Once in the BIOS, assuming that you have a BIOS that supports overclocking, (Retail manufacturers- Dell etc - tend to use bios's and mobo's that don't support o.c'ing), 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 speed, RAM timing, and RAM Ratio.
Basically, all you are trying to do is to get the highest FSB x Multiplier equation that you can get. 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 raise the FSB. This is self explanatory, and all of the RAM issues that have to be dealt with when raising the FSB are detailed 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, you can try lowering the multiplier in order to raise the FSB even higher. To understand this, imagine that you have a 2.13GHz processor that has a 266MHz FSB and a 8x multiplier. (266MHz x 8=2.13GHz). Obviously, that equation works as it's Tntel's stock frequency for the E6400, but there are other ways to get to 2.13GHz. You could raise the multiplier to 10 (cpu dependent of course) and lower the FSB to 213MHz, or you could raise the FSB to 355MHz and lower the multiplier to 6. These would both give you the same 2.13GHz that you started with. So both of those combinations should give you the same system performance. Correct?
(not real world figures, purely examples to make a point)
Not correct. 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 213MHz and raised the multiplier to 10, you would still have a clock speed of 2.13GHz, but the rest of the system would be communicating with your processor much slower than before resulting in a loss in system performance.
Really, you want to lower the multiplier in order to raise the FSB as high as possible. This sounds easy, but it isn't as you have to involve the rest of the system, since the rest of the system is dependent on the FSB as well, chiefly the RAM.
When you buy RAM, it is rated at a certain speed. For instance, DDR2 6400 is rated at 800mhz, DDR2 8500 is rated at 1066mhz
To understand these measures you need to 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 (slower) hard drive.
The thing to know is that RAM functions at a certain speed, which is a lot slower than the CPU speed. Most current RAM runs at speeds between 533MHz and 1066MHz.
This is because RAM manufacturers have also been able to do what cpu manufacturers have done, namely by sending information twice every RAM clock cycle.
(DDR2 stands for "Double Data Rate 2." DDR2 ram is an improved version of DDR ram that is faster and more efficient. Like standard DDR memory, DDR2 memory can send data on both the rising and falling edges of the processor's clock cycles. This nearly doubles the amount of work the RAM can do in a given amount of time).
So DDR2 800mhz means that the RAM operates at an effective speed of 800MHz, the "800" stands for the clock speed. Because it is sending instructions twice per clock cycle, that means its real operating frequency is 400MHz.
As stated above, when you raise the FSB, you effectively overclock everything else in your system. This applies to RAM as well. Problems can arise when you want to raise your FSB to speeds over 400MHz because the RAM is only rated to run at speeds up to 400MHz, raising your FSB higher than 400MHz can cause your system to crash. To solve this there are three solutions: using a FSB:Ram ratio, overclocking your Ram, or buying RAM rated at a higher speed.
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 DDR2 800mhz Ram that runs at 400MHz. But you want to raise your FSB to 450MHz to overclock your CPU. Obviously, your RAM will not like the raised FSB speed and will more than likely cause your system to crash. To solve this, you can set up a 5:4 FSB:RAM ratio. this ratio will mean that for every 5MHz that your FSB runs at, your RAM will only run at 4MHz.
To make it easier to work out, 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. This means that your RAM will only run at 80% of your FSB speed. So with your 450MHz FSB, running at a 5:4 FSB:RAM ratio, your RAM will be running at 364MHz, which is 80% of 450MHz. This is ok, since your RAM is rated for 400MHz.
(This isn't an ideal solution however. 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 is really quite 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.
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-6400 (DDR2 800) Ram at a speed of 410MHz, 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 worry. 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 BIOS's. 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. Basically, if you want to raise the speed of your RAM, you may have to raise the timings. It's not at all complicated. CAS latency is the minimum number of cycles the ram must wait before it can read or write again. The lower better obviously. (CAS4 would be better than CAS5 for instance).
Or instead of doing all of the above you could just buy ram rated at a higher speed, out of the box, at the rated speed you want to run your fsb. Say, again you want raise your fsb to 450mhz, just purchase ram rated to run at 450mhz (DDR2 7200 - 900mhz)
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. To solve this, you simply up the voltage to your CPU, also known as the vcore. Do this in the same way mentioned earlier in regards to the ram. 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. DON'T go past the recommended voltages.
Keep in mind that upping the voltage to your CPU will cause a lot more heat. This is why it is absolutely essential to have good cooling when overclocking.
Lastly, not all components overclock the same. You could have the exact, and i do mean exact same build as a friend but there is absolutely no guarantee yours will oc as far as theres. Each component is unique in its overclocking ability. But luckily, most are rather good or no-one would be doing it would they?
1) Once you reach the limit of the particular chip then thats it. There's nothing you can do to increase the o'c further.
2) A good form of stress-testing an overclock is by running Orthos for around 8 hours, if anything's going to fall over it'll be during the course of this.
3) Choose your motherboard wisely as motherboards can offer differing voltages to differing components making them friendly or not-so-friendly for oc'ing. Learn the default voltages for each component you intend to o.c as this will give you a starting point to see how well you'll be able to overvolt a particular component should you need to.
4) Read up on BIOS's, some make oc'ing a doddle, some can compound the difficulty.
5) Overclocking can be as financially dangerous as gambling, and just as addictive. So be careful!
Hope this is helpful to you all, if you've any questions shout up in the CPU's etc forum.