AMD Phenom (I) Overclocking Guide
A basic tutorial for overclocking using the HT (not the CPU multiplier) for the first generation AMD Phenom processor.
Index of Contents
Quick review of Phenom
Update: This guide covers the Phenom I processor, and does not cover the Phenom II, although the content may be applicable to that processor as well.
Phenom is AMD's desktop computer processor (CPU) originally launched in November of 2007. It is based on the K10 microarchitecture and is a native Quad-Core design, with all 4 cores residing on a single wafer. The Phenom I comes in two distinct models, the X4 and the X3, both designed for socket AM2+ motherboards (Phenom II processors are native to AM2+ and AM3 sockets). The Phenom X4 as you can guess is the Quad-Core processor. The X3, which came out later in March of 2008, is a triple-core processor. It is simply an X4 with one core hardware disabled. The X3 provides a route for AMD to sell X4's that had a faulty core. The X3 is priced in between the Athlon X2 and Phenom X4.
Here are some common terms I will use throughout this guide and a quick explanation of what they are.
Clock/Frequency: Used interchangeably with "speed". For example: CPU speed/clock/frequency is 2.4ghz.
Multiplier/Divider: Used in conjunction with the HT Bus Speed to determine what speed certain components run at. There is a CPU multiplier, an HT multiplier, an NB multiplier, and a memory/RAM multiplier.
HT Bus Speed: Default clock of 200mhz for all current Athlon 64 and Phenom platforms. Most other components base their speed from a multiplier/divider on this clock.
HT Link: This is the speed at which the CPU communicates with the North bridge chipset. Usually 1800mhz or 2000mhz.
NB Frequency: This is the speed that the North bridge operates at. Must be equal to or greater speed than HT Link. Usually 1800mhz or 2000mhz.
Memory Frequency: The speed that the memory operates at. DDR2-400, DDR2-533, DDR2-667, DDR2-800, and DDR2-1066 are the most common settings available here.
BIOS: Basic Input Output System. This contains all of the settings you will be working with during your overclocking foray. Generally accessed by tapping 'Delete' key during bootup.
Changes from Athlon 64
The Phenom shares much of the same functionality of the previous Athlon 64 processors. The memory controller is still on the processor as opposed to on the motherboard and it also shares the same pin layout and is compatible with AM2 motherboards (as long as the BIOS supports it). Overclocking is also much the same, with two big differences that I will highlight below.
On Phenom platforms, the memory speed is now determined by a multiplier on the HT Bus Speed. With Athlon 64 the memory speed was based off of the CPU speed, meaning if the CPU speed changed (adjusting the CPU multiplier for example) so would the memory speed. It also meant that certain processor speeds, such as 2100mhz, could not run at DDR2-800 due to the fact that the memory dividers could only be whole numbers. Rather than go into why that is, I will just say that with Phenom you no longer need to worry about that. Changing the CPU multiplier on a Phenom system no longer changes the memory speed. On a Phenom system, you will generally be presented with 5 options in the BIOS, which will vary by motherboard. My Gigabyte board gives me 2.00x, 2.66x, 3.33x, 4.00x, and 5.33x multipliers. They correspond to 400mhz, 533mhz, 667mhz, 800mhz, and 1066mhz. Some motherboard models may just display the speed instead of the actual multipliers used.
One other important addition to Phenom is that we now have a North bridge speed (NB Frequency). The NB speed can be set as well as the HT link speed. It is important to note that the NB speed must be equal to or greater than the HT link speed. It is best to leave them the same. Just like with the memory speed, the NB and HT link speeds can be shown as either a multiplier or as a frequency in the BIOS. 2000mhz, 2ghz, and 10x all correspond to the same speed, where 10x is a multiplier (10 x 200mhz = 2000mhz). It is the preference of the motherboard maker how it is displayed. Available speeds usually range from 1000mhz to 2000mhz.
There are several programs you will want to acquire before overclocking. I have made a list with links to their respective websites:
CPU-Z - This program will display all of the important system settings.
PC Wizard - This program will also display system settings, but it is also useful as a temperature monitor. When minimized it can display all of the major system temperatures in text that can be set to stay above all other windows.
Prime 95 v25.6 - Useful for its "Torture Test". Will automatically stress all cores available to 100% CPU load. This is used to test if the system is stable.
Once you have acquired all of these programs you will be ready to start overclocking
The Fun Part
You will want to reboot the computer and tap the Delete key repeatedly until you are presented with the blue BIOS screen. Now every BIOS is different so I will be using general terms. You will want to find the BIOS menu that is related to overclocking or changing system settings for the CPU, memory, etc. Hopefully your BIOS has options to change all of the multipliers, speeds, and voltages. If not, then you may be out of luck.
The first step is to find the motherboard HT Bus Speed limit. This step is actually optional, and you can go straight to finding the CPU limit if you want, but I do recommend finding the HT Bus max speed, so there is no confusion later on when finding the CPU max speed. So adjust the CPU multiplier, memory/ram multiplier, NB multiplier, and HT Link multiplier all down to their lowest settings (making sure to keep the NB and HT Link running at the same speed). Now increase the HT Bus Speed. How much you increase it is up to you, I usually start at 240mhz, since any motherboard should have no problems at that speed. Once you have increased your HT Bus Speed, go to Save and Exit to reboot the computer. You may want to boot into Windows and run a stress tester, but it isn't necessary at this point. If the computer successfully boots, go back into the BIOS and increase the HT Bus Speed another 10mhz. Keep doing this until you get to 280-300, and then use increments of 5mhz, and run a stress test between each boot. When the computer starts failing the stress test, or it fails to boot, you have found the motherboard's limit. If the computer fails to boot you may have to use the CMOS Clear jumper on the motherboard, just follow the directions in the motherboard manual.
Now that you have found the motherboard's limit, it is time to find your CPU's max speed. Most Phenoms will do between 2600mhz to 3200mhz, cross your fingers that you got a good one. Bring the HT Bus Speed back to the default 200mhz, and keep all multipliers low except put the CPU multiplier back to the default, which will vary depending on the processor you have. For a 2.1ghz Phenom it will be 10.5x, 2.2ghz Phenom it will be 11x, and so on. Start by increasing the HT Bus Speed by 10mhz increments. Once you reach a CPU speed of 2600mhz you will want to go down to 5mhz increments or so, and start doing stress testing in between each speed increase. Using Prime95 to stress test, run it for about 20 minutes. If there are no errors keep going. Once you do get an error, it does not mean your system is going to crash, however it is not 100% stable. Try increasing the CPU voltage by 0.025v. Usually there is a setting in the BIOS to change the CPU voltage. Default for Phenoms is 1.25V to 1.30V, depending on the model. As a side note, I recommend disabling Cool n' Quiet, as it could possibly cause instability when overclocking (Cool n' Quiet automatically lowers voltage and CPU multiplier based on system load). If increasing voltage by 0.025 made it stable, keep overclocking. You won't want to go higher than 1.45v, unless you have very good cooling and are ok with reducing the life span of your CPU. Once you have reached your goal or cannot go any higher without instability, run Prime95 for an hour or more to make sure your system is stable. If it is, good job!
At this point you can adjust your memory, HT Link, and NB multipliers to bring those speeds back as close to their default as you can. Or you can attempt to overclock those components as well. This, however, will not be covered in this guide. So congratulations on your new overclock. Here is a CPU-Z screenshot of my Phenom X3 after successfully overclocking it (click the thumbnail). Achieving this clock speed at that voltage is not common, but if you're lucky you'll have similar results.
Overclocking your system components will generally void any warranty they carry, so be mindful of that. Anytime you run a component outside of its rating you are risking damage to it. This guide is merely a tool for those willing to take this risk, and the writer (me) cannot be held responsible if you mess up your computer or fry a component.