A Beginner's Guide to Overclocking

This guide has been created from an AMD point of view, but Intel'ers can use this as well.

Warning: Overclocking isn't always safe. There are safety measures built in to your computer to prevent damage while overclocking, but the safety of your hardware isn't guaranteed (even if you are following the guide).​

The main pieces in your computer that are affected by overclocking are your CPU, your memory, and your motherboard (but you won't have to worry about your motherboard if you're just beginning to overclock). When you overclock your CPU, you also end up overclocking your Memory, HT link (if you have one), sometimes your AGP/PCI-e and PCI cards, and a few other things. Why? Because of a magical thing called "FSB".

What is FSB?
FSB, as far as overclocking is concerned, is simply a number. Your computer's FSB is the data links between your CPU, Memory, Chipset, and other components. Lots of things in your computer use the FSB to tell it how fast to run. FSB is usually rated in MHz.

How does my CPU use FSB?
Your CPU takes the FSB and multiplies it by the CPU Multiplier to get your CPU speed.
In math? FSB (in MHz) times Multiplier equals CPU speed (in MHz)

How does my Memory use FSB?
Your memory takes that FSB speed, multiplies it by two (DDR=Double Data Rate), and it gives you your DDR rating.
Sometimes, the processor wants to set the FSB at a high value, but the memory wants to set the FSB at a low value. The motherboard will set a "Divider" that will lower the Memory's FSB so that the Memory can run at the lower speed it wants without affecting the CPU. The Memory Divider is also known as the Memory Ratio.
In math? FSB divided by the memory ratio times two equals DDR Rating.

Why is PC133 so much slower than PC2100. Don't they run at the same FSB?
Yes, they run at the same FSB, but PC133 isn't DDR (and it's older technology).

Wait.. Didn't you say something about a CPU Multiplier? Can't I change that?
Yes. You can change your CPU multiplier, too. Some processors, such as AMD's Sempron, won't let you increase this, though. If you want to overclock your computer, but don't want to change the FSB, you can change the CPU Multiplier. The advantage of changing this rather than your FSB is that the CPU Multiplier only affects the CPU. FSB, like I said before, affects more than your CPU.

Lets make it even more complicated!
Remember FSB? FSB is (and now "was") the link between your CPU, Memory, Chpiset, AGP/PCI-e, and other computer components. As computers started to run faster and faster, a lot of motherboards started getting bottlenecked at these points, so we now have AMD's HyperTransport Technology and Intel's QuadPumped Technology to fix it. Although AMD was the company to bring HyperTransport to fame, AMD, Apple, nVidia, Cisco Systems, Sun Microsystems, and a few other companies all helped develop HyperTransport (HT). HyperTransport links were designed to replace the FSB system. This means that the links between your CPU, Memory, Chpiset, AGP/PCI-e, and other computer components are now three to five times faster than the original FSB system was.
Although HyperTransport was designed to replace the FSB, it hasn't eliminated it. Socket 754's use 4x FSB and Sck939 use 5x FSB. Making your HT Link run faster doesn't make your computer faster, it just gives it the potential to be faster. Making this run too fast will crash your computer.
(Intel plans to release a competitor to HyperTransport that they're calling the Common System Interface (or "CSI"). This is expected in 2008.)
In math? FSB times the HT Multiplier equals the HT Link Speed (or sometimes called "Rated FSB").

Wait! I still don't understand HyperTransport/QuadPumped! And why doesn't it make my computer faster?
The CPU, Memory, Video Card, chipset, and everything else in your comptuer all need to be able to talk to eachother, right? Think of the data paths that link all those things together as highways. If you try to fit too many cars down the highway, you get a traffic jam and some cars have to wait before they can get through. HyperTransport puts more lanes in the highway so more cars can flow through it. If you have two lanes, but only one car is going down the highway, adding a third lane won't make that car go faster. If you have a few thousand cars, but only two lanes, adding a third lane would make the flow move faster.

What about Intel! Don't they have, like, 1GHz FSB?
Those 800MHz FSB Prescott P4's actually run at 200MHz FSB. Intel also had the same problem with the FSB not being fast enough to support the system. Intel's Pentium 4 line of processors (for example) has their FSB "QuadPumped", which offers the same advantage as HyperTransport. I believe that this is the same story with the "1GHz FSB" Intel processors. If you look at CPU-Z, you should have both FSB and "Rated FSB". For overclocking purposes, we'll only be concerned about the original FSB.
Also, there are rumors that Intel's QuadPumped Technology does not increase the link speed between multiple processors whereas AMD's HyperTransport does. Given Intel's plan to move to a mainstream Quad Core, a HyperTransport competitor by Intel (aka: Intel's CSI Bus) suddenly makes sense.

I'm a visual learner. Can you show me a picture?
Lets use one that I randomly pulled off of Google's image search.


The image (that should now show up correctly) above represents a Quad Processor AMD Opteron computer (Intel is similar). There is a 6.4GB/s link between each processor and a 6.4GB/s link between the processors and the AMD-8131 Northbridge chipset. The Northbridge connects to the PCI Express bus, SCSI controller, and on-board Ethernet cards. The Northbridge is also connected to the AMD- 8111 Southbridge chipset via a slower 800 MB/s link. The Southbridge connects to slower on-board devices like the on-board audio, USB 2.0, EIDE, etc. This was FSB's job until today's devices became too fast for it. System devices would end up competing for bandwidth. And what shows up like a knight in shining armor? HyperTrasport and QuadPumped Technology.

Lets do some math!! Can we have an example?
When stock, my computer runs at 200 FSB. The CPU has a 10x Multiplier. The memory is PC3200 and isn't divided (We call this a 1:1 ratio, or a 1/1 divider). The HyperTransport link runs at a 4x Multiplier. Now that we know all that...

Lets find the CPU speed.
200MHz FSB times 10 (CPU Multiplier) = 2,000 MHz CPU speed, or 2GHz CPU speed.

Lets find the Memory speed.
200MHz divided by 1 times 1 (remember the divider?) times two (Double Data Rate) = DDR400. We can also take that DDR400 and multiply by 8 bytes to give us 3200, or PC3200.

Lets find the HT speed.
200MHz times 4 (the HT Multiplier) = 800MHz HT Link.

Put all that together, and you can see that I have a 2GHz CPU, DDR400 memory, and an 800MHz HT link.

So what happens when you raise the FSB?
Lets say I take my computer and run it at 220 FSB. Lets do the example again.

CPU:
220 FSB times 10 (Multiplier) = 2,200MHz, or 2.2GHz. (See the increase?)

Memory:
220 FSB divided by 1 times 1 (1:1 ratio) times two (DDR) = DDR440, or about PC3600

HT:
220 FSB times 4 (HT Multiplier) = 880MHz HT Link

At stock speeds, we had:
200FSB, 2.0GHz, DDR400, and 800MHz HT.
Overclocked, we have:
220FSB, 2.2GHz, DDR440, and 880MHz HT

What if you just raise the CPU Multiplier?
Lets say I raise it to 11.
CPU:
200 FSB times 11 = 2,200MHz, or 2.2GHz.
Memory:
200 FSB divided by 1 times 1 times two = DDR400 or PC3200
HT:
200 FSB times 4 = 800MHz HT Link

200 FSB, 2.1GHz, DDR400 and 800MHz HT
Notice how everything is at it's original speed except the CPU.

Memory dividers are really confusing. Why would I ever want to make my memory run slower? Could you give me an example?
Sure! Lets say your memory runs at 200 FSB, but can only run at a maximum of 210 FSB before it crashes. We can set a Memory Divider of 5/6 to drop it down from 200 FSB to 166 FSB. Now we can raise your FSB higher without stressing out your memory as much.

200 FSB divided by 6 times 5 times two = DDR333

240 FSB divided by 6 times 5 = DDR400 (Back to where we started, but the FSB is a lot higher and the memory is still in a safe range.)

How do I know when to stop?
When your computer will not boot in to Windows (or if it does, will freeze after a few minutes of gaming), you'll know that you have pushed something too far. If you've overclocked to the point where your computer unstable, you can boot into the BIOS and set your FSB back down. If you overclock too far your computer may not boot at all. If your computer does not do anything when you turn it on, you'll need to reset the BIOS. You can do this by unplugging your power cable and removing the silver button battery on your motherboard. Leave it out for at least 5 seconds (15 seconds recommended) and then put it back in. Plug in the power cable and boot. You'll need to go into your BIOS and load the default settings.
An alternative to changing the FSB in the BIOS is to change the FSB with a program such as ClockGen. When your computer crashes, the actual BIOS value doesn't change, so you reset to stock speeds every time you reboot. Once you've found an overclock that works for you, you can try setting it in the BIOS.

Another thing that could stop your computer from running (and could potentially damage your computer) is heat. Overclocking means more power. More power means heat. If your CPU, Memory, or motherboard chipset(s) become too hot, they will stop working properly. Overclocking is not recommended on stock CPU coolers. While overclocking, always watch your temperatures! If something becomes too hot, do anything you can to cool it down before you try overclocking again. Most things can be easily cooled by simply adding a fan to blow over it.

I can't raise my FSB anymore! Is this really as fast as my computer will ever go?
The exciting answer is "No"! Just because your computer has hit it's limit doesn't mean that everything in your computer has hit it's limit, but rather that one thing in your computer has hit it's limit. If you can figure out what thing that is, you can usually make that one thing run a little slower. For example, if your memory is what's crashing but your CPU can run faster (this is common), you can use the Memory Divider to lower it. With the memory running a notch slower than usual, you can increase your overclock even more.

You'll need to learn a lot more about overclocking if you want to go to the extremes that you see in "The Extreme OC Clubhouse".

How can I check what my computer is running at now?
Try using CPU-Z. CPU-Z will let you look at all the fun little numbers that make your computer tick without running the risk of accidentally changing something.

Okay! I'm confident that I know what I'm doing. Where do I change my FSB?
Your FSB (and everything else to do with overclocking) is located in your BIOS. Be careful, though. There are a lot of settings in here that shouldn't be played with. Different motherboards will have the FSB in different places. If you can't find your FSB, it may be disabled from the BIOS. You can try asking people in the forums, but each BIOS is unique to their manufacturer. If all else fails, try using ClockGen. ClockGen runs inside Windows and can support a good range of motherboards.

If you have any questions, ask!

 

Haven't read through it yet really but I don't think we have an overclocking guide so I vote that this gets a sticky. Remember to do your best to keep it up to date though. Also, in theory it isn't the FSB on AMD64 systems but as a general guide this should be ok.

 

This is a good versatile guide for overclocking all computers. Talk to a mod, or a super mod and request a sticky. It goes well with my AMD 64 specific guide. Good job!

 

I hate to admit it, but I'm still stuck back in Socket-754-world. I just noticed that TPU had a lot of people flooding the OC forums asking how to overclock. I'm just trying to help keep the forums clean.

 

Thats the exact same reason I posted mine. With yours and mine, the OC traffic seems to have slowed down.

 

Nothing wrong with S754... I still use it myself! I personally would refer to it as FSB like you have but in reality I think it's called the hyper transport or something like that. Either way, as far as overclocking is concerned they work in a similar way.

Edit: my 754 board does call it FSB and I believe others do to but it is wrong

 

Eh.. I'm going to have to disagree slightly with you there. From what I understood, HyperTransport was the link between the CPU, Memory, Chipset, PCI-e/AGP. I suppose you're right in the sense that it replaced FSB as the link between these components, but it hasn't been eliminated. HyperTransport is based off of the system's FSB, after all.

I'm reading up on it over on Wikipedia. Isn't it just a beefed up Front Side Bus (emphasis on bus)?

Edit: From what I understand from Wikipedia, it's more of an enlarged bus that sort-of works on top of FSB, replacing the actual bus side.

Lets see if I can hotlink this image.

The HT link, as you say, replaces the FSB. But the HT link is still based off of the system's FSB. I suppose we're both right. Call it a draw?

P.S. I still love my S754 board, but I can't find any Athlons for it! Only Semprons.

 

I vote if anything... cut and paste to the AMD sticky. The only mention of Intel was this "unbiased" statement.

 

I never said it was unbiased.

I'm not much of an Intel person, but I'm guessing Intel's "QuadPumped FSB" works the same as HT, correct? How do the Core 2 Duo's do it? I heard nVidia's Intel chipsets use HyperTransport.


Edit: The guide has been de-biased. I just didn't feel like writing the Intel section when I wrote it. It's a work in progress, right?

 

STICKY IT!!! FSB is equivalent to HT speed; both just marketing rubbish.

 

yes, please sticky it.
Reading all the info has helped me understand a lot about o.c'ing. Considering that i'm still a virgen o.c'er. With all the info I feel that I could twek my system a little at a time to bring out the monster inside. Even tho i'm still on a socket A board. I'm willing to push it a little.
Hay, if all else fales a new board and cpu combo don't coast that much........right.

 

I vote that we have a Wiki now for these things.

 

From what I understand (and I've read many articles on this) AMD boards have BOTH an FSB and the Hypertransport Link. The HT link connects the chipset (NB and SB) and the CPU together. The Front Side bus connects everything else, PCI, PCI-E, memory etc. The Hypertransport runs at a multiplier of the FSB just like the CPU does.

That is my understanding.

 

It's true to its word a beginners guide, sweet i shall read more as it comes , not that i have a machine capable of O.C'ing , very intresting never the less lol.

 

Surely the forums can still be used for guides? If people are looking for overclocking guides they'll probably come to the Overclocking and Cooling forum first. I can see where you're coming from, but I think if it's going to work like that all the guides that have been stickied should be moved to the Wiki and then unstickied so everything is in one place, rather than being dotted around. I don't mind copying a few of the guides into the Wiki sometime.

 

It's not a bad guide at all, I used its assistance in OCing my Sempron system. And even if you are using an Intel Processor, it still gives you the basics of how to go about OCing, or so it seems to me anyways.

 

In the bios setup for my system, 939 mobo amd fx 60.. it states I can have a multiplier from 13 to 25 but I cannot get to any values in the screan, what is up?

 

Is it an OEM system (ie from a company like Dell or HP)? They often lock the BIOS to prevent overclocking.

 

no it is a barebones ASYS mobo 939.. but I did get a fractional increase my second try by at oc'ing 205fsb

 

If you can't find anything in your BIOS to change your multiplier, try searching google. Motherboards sometimes have "hidden settings" that can be unlocked by pressing ctrl+shift+F1, or some odd combination like that. If you still can't find it, your motherboard's manufacturer might have disabled it. Try upping the FSB 5 MHz at a time and like I say, watch your temperatures. If your motherboard really won't let you change your multiplier, then all you can really do is look for a better motherboard next time you build a computer.

 

yep, afterreading I found it, up to 14 playingwith the volts /fsb etc.. at one point was at 210 but now the sys will not allow me to set above 200! okk, I am stable at 205, no real need to oc, just having some fun...

 

I think we have too many stickies...

... as a matter of practice... I think stickies should move to the WIKI

P.S.
@16, thanks for putting the time into your post!

 

It took me a while to figure out who "16" was.
Thanks! Sometimes, I just like writing.

 

found out my bios was locked so i wanted to get a program that could oc fsb in windows.
i have an intel e6600 2,4 ghz processor and need my clock generator. i cant open the bos...my parents wont let me...stupid...well so i wondered does all processors of same model have same clock gen? i mean can a guy that has same processor as me check his clock gen and then i have same as he??? plz help me my bios is locked!!!

 

Will raising latencies on my Centron duel channel 1g chip, 2.5 3 3 7 help me push my very low 210 fsb higher?