Edited on 08-Jun-2008: Guide is now version 1.7 – added a 2nd example minimizing the vcores on my system.

Before you continue, I wrote this guide with the newbie in mind, so please don't reply criticizing it for being too simplistic -- it's this way by design. Also know that the steps for overclocking apply to all chips: quads, duals, single-cores, or triple-core processors. You can use the basics taught in this guide with any modern machine.

I wrote the guide originally using a Q6600/Asus P5B-Deluxe, but recently sold that machine and upgraded to an X3360/DFI LT P35-T2R. I didn’t want to change the first half of the guide, so it’s still based on the Q6600/Asus board. The newly written section about finding a minimum stable CPU and MB vcore section is written based on my actual experience finding stable settings for this newer machine. Again, the steps for overclocking are pretty independent of this subtle change. Finally, I take no responsibility for what you do with the information in this guide. Overclock your hardware at your own risk.

Overlocking Basics

Before you start, read your motherboard manual. Know how to reset your BIOS in the event that you are too aggressive in your CPU settings and it doesn't complete a POST (Power On Self Test, that beep when you first turn the machine on and it starts up means you passed the POST). Some motherboards reset automatically if you switch off the power supply for 30 seconds or so. Others require you to move a jumper to reset them.

The basic formula you need to know for CPU speed is:

CODECPU Speed = CPUM x FSB
where CPUM is the CPU Multiplier, and FSB is the front side bus.

Example: The Q6600 runs at a factory setting of 2.40 GHz. That's the product of a 9x multiplier and a 266 MHz FSB (quad pumped it's 1066 MHz but we're not quad pumping these numbers). So CPU Speed = 9 x 266 which is 2,394 MHz or 2.40 GHz.

Below is a list of Intel chips. Most of them, including the Q6600, have a "locked" multiplier – meaning it can't go above a certain value (9x in this case). The only way to increase the CPU speed beyond the stock value is by raising the FSB. Other "Extreme" chips like the QX9650 or X6850 have “unlocked" multipliers; you can raise their multipliers above the stock value. These chips are denoted from the standard stock by the letter “X” in their model number.

For reference, here are all Intel offerings as of May/’08:

QUOTE
Quads:
QX9775: 8.0x400 = 3.20 GHz
QX9775: 8.0x400 = 3.20 GHz

Q9300: 7.5x333 = 2.50 GHz
Q9450: 8.0x333 = 2.67 GHz
Q9550: 8.5x333 = 2.83 GHz
QX9650/QX6850: 9.0x333 = 3.00 GHz

Q6600: 9.0x266 = 2.40 GHz
QX/Q6700: 10.0x266 = 2.67 GHz
QX6800: 11.0x266 = 2.93 GHz

Duals:
E6540/50: 7.0x333 = 2.33 GHz
E6750: 8.0x333 = 2.67 GHz
E8190/8200: 8.0x333 = 2.67 GHz
E6850/8400: 9.0x333 = 3.00 GHz
E8500: 9.5x333 = 3.16 GHz
E8300: 8x333 = 2.83 GHz

E6400/20: 8.0x266 = 2.13 GHz
E6600: 9.0x266 = 2.40 GHz
E7200: 9.5x266 = 2.53 GHz
E6700: 10.0x266 = 2.67 GHz
X6800: 11.0x266 = 2.93 GHz

E2140: 8.0x200 = 1.60 GHz
E2160/E4300: 9.0x200 = 1.80 GHz
E6300/20: 7.0x200 = 1.86 GHz
E2180/E4400: 10.0x200 = 2.00 GHz
E2200/E4500: 11.0x200 = 2.20 GHz
E2220/E4600: 12.0x200 = 2.40 GHz
E4700: 13.0x200 = 2.60 GHz
X7800: 13.0x200 = 2.60 GHz
X7900: 14.0x200 = 2.80 GHz

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Added (02.01.2009, 1:24 Am)
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My first quad system was based on a Q6600 at 9x333=3.00 GHz (25 % over factory). I found the max it can go when cooled with air is 9x370=3.33 GHz (39 % over factory), but it just ran too hot for me. Every chip is different... you might be an unlucky owner of a chip that just doesn’t overclock very high at all.

Overclocking is more complicated than just adjusting two settings in the BIOS, because as you increase the FSB, you'll also need to increase the core voltage (vcore) which is the actual juice going to the processor. As well, you may have to increase the other voltages on the board like: memory, FSB, NB, SB, ICH chipset. There are also parameters controlling your memory that may need tweaking as well. Don't worry about them for now. The board can manage these automatically which is what you should do initially. When you finally decide on an overclock number, you'll want to go back and minimize your voltages to minimize your heat production. We'll get into this later. For now, you want to verify you can successfully POST, and verify that your system can run stable at the settings you've selected.

Pre-Overclocking Checklist

Before you think about overclocking your system, you'll need to be sure you're using quality parts that can handle the increased stresses.

1. Motherboard
I decided not to maintain a list of motherboards that are known to be good overclockers; keeping the list updated would be too time consuming. I only mention this because if you’re using some generic MB you got free with the purchase of your CPU, you’re probably not going to be able to overclock it.

Added (02.01.2009, 1:26 Am)
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2. Cooling
Cooling is very important since you're asking the system to produce more heat than it's designed to produce. A quad core chip will produce twice the heat of a dual core chip, so if you're using the Intel Stock HSF, you'll probably want to upgrade to something better. Again, I don’t wanna maintain a list. I can tell you that I am using a Thermalright Ultra-120 Extreme and am very happy with it.

Here is a more recent list of HS’s that have actually been reviewed and ranked based on performance.

Finally, there is a section at the end of the guide entitled, “Temperature Management” which I would strongly suggest you at least have a look at since it contains some good info. For example, for under $5 you can probably shave off ~10-15 % of your NB (North Bridge) load temps simply by adding a small fan to the heatsink even if it was never designed to have one (attach it with a zip tie):

Reduced: 85% of original size [ 600 x 443 ] - Click to view full image

3. Memory
You will need memory that can keep up with your overclocked system. Again, I’m not going to keep a list. You’ll see RAM listed with timings and speeds that I’ll decode for you using the following examples:

QUOTE
DDR2-800 (PC2-6400) 4-4-4-12
DDR2-1066 (PC2-8500) 5-5-5-15

• The first part is self-explanatory (DDR2 memory).
• The number after it is the data transfer rate. Simply divide it by 2 to get the maximum FSB speed for which the module is rated. Example: 800/2 = 400 MHz. Therefore, DDR2-800 can work on systems with a FSB of up to 400 MHz (anything more and you’re lucky).
• The PC2-XXXX is designation denoting theoretical bandwidth in MB/s. Some memory manufactures use this instead of the DDR2-xxx designation. You can calculate it for any FSB you want by simply taking the FSB and multiplying by 16 (rounded in some cases). Example using a 400 MHz FSB: 400x16=6400. So you’d need at least PC2-6400 to run on a FSB of 400 MHz.

The numbers after that are the main timings (clock cycles). In general, the lower these numbers are, the faster the memory. For more on memory timings, see this page.

QUOTE
DDR3-1333 (PC3-10666) 9-9-9-24
DDR3-1600 (PC3-12800) 7-7-7-20

•

Added (02.01.2009, 1:27 Am)
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The first part is self-explanatory (DDR3 memory).
• The number after it is the data transfer rate. Simply divide it by 4 to get the maximum FSB speed for which the module is rated. Example: 1600/4 = 400 MHz. Therefore, DDR3-1600 can work on systems with a FSB of up to 400 MHz (anything more and you’re lucky).
• The PC3-XXXXX is designation denoting theoretical bandwidth in MB/s. Some memory manufactures use this instead of the DDR3-xxxx designation. You can calculate it for any FSB you want by simply taking the FSB and multiplying by 32 (rounded in some cases). Example using a 400 MHz FSB: 400x32=12800. So you’d need at least PC3-12800 to run on FSB of 400 MHz.

4. Power Supply
There are really two major factors to consider when selecting a power supply:

1) Quality of the PSU
2) Power output

I don’t have the expertise to write up this selection of the guide, so I’ll point you to this nice list written by perkam to use as a guide. More recently, TH.com wrote another article you can check out on the topic.

There is a great article on power consumption over at TH.com that I suggest you read at your leisure. I distilled out some highlights to underscore how much power systems really use: