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Overclocking --CPU, NB/HT-link-- Phenom II X4
2010-05-29 3:27 PM PDT
For this quasi-advanced overclocking tutorial, assuming the overclocker knows the basics, I am using an AMD Phenom II X4 Socket AM2+ 940 BE CPU w/an ASUS M3A32-MVP Deluxe motherboard w/the 790FX NorthBridge and SB600 SouthBridge.
CPU overclock settings
The AMD Phenom II 940 BE is 3.0GHz from factory in which the speed is determined by multiplying the FSB (Front Side Bus) setting (200 by default) and the CPU multiplier. If you do not own a Black Edition CPU, the CPU multiplier will be locked meaning you have to increase the FSB in order to overclock your CPU, but, by doing this, you also overclock your RAM (memory) as its speed is determined by the FSB x Memory Divider. Thus, if you have to increase the FSB, adjust the memory divider accordingly to avoid running your memory faster than what it can support. Memory settings are explained in greater detail on my other overclocking guide for Athlon X2s.
Now, assuming we don't want to mess around w/the FSB speed, we can use the BE--Black Edition--unlocked multiplier to make the CPU faster. You should be able to go from an overclock of 0% - 29% using your stock cooler. Phenom II 940 X4 CPUs are stable @ 3.4GHz w/no voltage increase.
To go above 3.4GHz, you will need to voltage bump the CPU. Socket AM2 Phenoms are, generally, stable up to 3.8GHz @ 1.52v but I do not like running that much voltage and possibly shortening my CPU life-span so I run it at 3.4GHz w/the stock voltage setting of 1.35v. For the 3.4 - 3.7GHz range, you should be running the voltage around 1.45v; 3GHz - 3.4GHz @ stock voltage or below if you can, 3.4GHz - 3.6GHz @ 1.35v to 1.4v, 3.6GHz - 3.8GHz @ 1.4v to 1.45v, 3.8GHz - 4GHz @ 1.45v to 1.5v, and anything above 4GHz @ +1.55v if you're feeling froggy.
They say that in order to avoid bottlnecking a CrosssfireX rig, you need your Phenom II X4 @ 3.8GHz or higher but this is incorrect. As of late, I've been running my Phenom @ 3.4GHz w/two HD4870s and the CPU has never been above 75% usage under heavy game load. It's usually around ~50% for Steam/Valve games and around ~35% for non-Steam/Valve games. Maybe if I was running two HD5870s, the story would be different.
Another possibility for not needing such a high CPU clock for my two cards to run w/out being bottlenecked (like it would matter anyways when you're running this kind of power for TF2 and L4D2--I didn't like Crysis--but for arguments sake) is possibly my PCIE bus being clocked @ 125MHz, up from the default 100MHz--DO NOT OVERCLOCK THIS IF YOU ARE NEW. PCIE overclockers usually go no higher than 110MHz. If you're not careful, you'll fuck up your hard drive(s) by overclocking this. Personally, I'd still do it just to see what it did but most people shouldn't because a 10MHz bump on 100MHz isn't much of a show stopper.
However, I noticed a pretty big gaming bump from the extra 25MHz; the 25% increase was hard to describe but a seasoned gamer would be able to tell easily and my boot times got faster. I haven't juxtaposed this w/a 10% increase since I have an uber chipset that gives me +25% just for knowing about the feature and where it was in BIOS. I have to admit, though, I've tweaked so many things that I was wondering if I should unplug all of my storage hard drives before I enabled it--I did but I didn't like it! ha
The 790FX chipset comes w/something called AutoXpress which handles all of the nitty gritty w/out affecting my CPU overclock or NB overclock either. It just affects the PCIE bus which is pretty cool and I didn't fry my hard drives so that's a plus. My computer booted faster but I didn't really care about that because it already boots fast.
NB-link and HT overclock settings
The CPU-NB (NB-link) verbage pertains to a section of the CPU which controls the L3 cache, Memory Controller and the Hyper-Transport (HTT). Think of him as Second-in-Command behind the CPU. The NB-link and HT have separate BIOS multipliers; the NB-link MUST be equal to or higher than the HT speed! For example, my current settings are the NB-link @ 2400MHz and the HT @ 2000MHz.
The North Bridge and Hyper Transport can be overclocked separately as you see from my aforementioned example. If you have the HT speed above the NB-link speed, you are a moron and will get an unstable POST (Power On Self Test) during power-on load and possibly have to reset BIOS via CMOS. To prevent that from happening, leave the NB and HT link speeds alone. Mess w/that after you figure out your CPU overclock.
However, say, for example, you overclock the NB-link @ 2400MHz, which is normally 1800MHz for an AM2+ Phenom II 940 X4 socket 790FX motherboard, you will have just made whatever RAM you have faster than before w/no affect on causing RAM induced system instability. I benched my DDR2-1066 Corsair Dominator 2x2GB kit @ 5-5-5-15-22 2T against my brothers DDR3-1600 2x2GB kit w/his NB-link left stock @ 2000MHz for AM3 socket motherboards and Phenoms while using the same CPU speeds respectively. I was surprised to see both RAM kits scored virtually the same benchmark score; yowsa. Increasing the HT speed had no affect on performance so I set that to 2000MHz, up from the stock 1800MHz of AM2 socket Phenom II 940s.
Most NB-links on AM2 motherboards are stable up to 2400MHz w/no over-volting required however this may vary. Most AM3 motherboards are stable up to 2600MHz w/no over-volting. If you're worried at first and have low motherboard temperatures, give them a 0.1v bump to ensure stability and turn it down later after you've tested stability just to see if you need that 0.1v bump.
/This guide may or may not be appended in the future. Hmm.
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CPU overclock settings
The AMD Phenom II 940 BE is 3.0GHz from factory in which the speed is determined by multiplying the FSB (Front Side Bus) setting (200 by default) and the CPU multiplier. If you do not own a Black Edition CPU, the CPU multiplier will be locked meaning you have to increase the FSB in order to overclock your CPU, but, by doing this, you also overclock your RAM (memory) as its speed is determined by the FSB x Memory Divider. Thus, if you have to increase the FSB, adjust the memory divider accordingly to avoid running your memory faster than what it can support. Memory settings are explained in greater detail on my other overclocking guide for Athlon X2s.
Now, assuming we don't want to mess around w/the FSB speed, we can use the BE--Black Edition--unlocked multiplier to make the CPU faster. You should be able to go from an overclock of 0% - 29% using your stock cooler. Phenom II 940 X4 CPUs are stable @ 3.4GHz w/no voltage increase.
To go above 3.4GHz, you will need to voltage bump the CPU. Socket AM2 Phenoms are, generally, stable up to 3.8GHz @ 1.52v but I do not like running that much voltage and possibly shortening my CPU life-span so I run it at 3.4GHz w/the stock voltage setting of 1.35v. For the 3.4 - 3.7GHz range, you should be running the voltage around 1.45v; 3GHz - 3.4GHz @ stock voltage or below if you can, 3.4GHz - 3.6GHz @ 1.35v to 1.4v, 3.6GHz - 3.8GHz @ 1.4v to 1.45v, 3.8GHz - 4GHz @ 1.45v to 1.5v, and anything above 4GHz @ +1.55v if you're feeling froggy.
They say that in order to avoid bottlnecking a CrosssfireX rig, you need your Phenom II X4 @ 3.8GHz or higher but this is incorrect. As of late, I've been running my Phenom @ 3.4GHz w/two HD4870s and the CPU has never been above 75% usage under heavy game load. It's usually around ~50% for Steam/Valve games and around ~35% for non-Steam/Valve games. Maybe if I was running two HD5870s, the story would be different.
Another possibility for not needing such a high CPU clock for my two cards to run w/out being bottlenecked (like it would matter anyways when you're running this kind of power for TF2 and L4D2--I didn't like Crysis--but for arguments sake) is possibly my PCIE bus being clocked @ 125MHz, up from the default 100MHz--DO NOT OVERCLOCK THIS IF YOU ARE NEW. PCIE overclockers usually go no higher than 110MHz. If you're not careful, you'll fuck up your hard drive(s) by overclocking this. Personally, I'd still do it just to see what it did but most people shouldn't because a 10MHz bump on 100MHz isn't much of a show stopper.
However, I noticed a pretty big gaming bump from the extra 25MHz; the 25% increase was hard to describe but a seasoned gamer would be able to tell easily and my boot times got faster. I haven't juxtaposed this w/a 10% increase since I have an uber chipset that gives me +25% just for knowing about the feature and where it was in BIOS. I have to admit, though, I've tweaked so many things that I was wondering if I should unplug all of my storage hard drives before I enabled it--I did but I didn't like it! ha
The 790FX chipset comes w/something called AutoXpress which handles all of the nitty gritty w/out affecting my CPU overclock or NB overclock either. It just affects the PCIE bus which is pretty cool and I didn't fry my hard drives so that's a plus. My computer booted faster but I didn't really care about that because it already boots fast.
NB-link and HT overclock settings
The CPU-NB (NB-link) verbage pertains to a section of the CPU which controls the L3 cache, Memory Controller and the Hyper-Transport (HTT). Think of him as Second-in-Command behind the CPU. The NB-link and HT have separate BIOS multipliers; the NB-link MUST be equal to or higher than the HT speed! For example, my current settings are the NB-link @ 2400MHz and the HT @ 2000MHz.
The North Bridge and Hyper Transport can be overclocked separately as you see from my aforementioned example. If you have the HT speed above the NB-link speed, you are a moron and will get an unstable POST (Power On Self Test) during power-on load and possibly have to reset BIOS via CMOS. To prevent that from happening, leave the NB and HT link speeds alone. Mess w/that after you figure out your CPU overclock.
However, say, for example, you overclock the NB-link @ 2400MHz, which is normally 1800MHz for an AM2+ Phenom II 940 X4 socket 790FX motherboard, you will have just made whatever RAM you have faster than before w/no affect on causing RAM induced system instability. I benched my DDR2-1066 Corsair Dominator 2x2GB kit @ 5-5-5-15-22 2T against my brothers DDR3-1600 2x2GB kit w/his NB-link left stock @ 2000MHz for AM3 socket motherboards and Phenoms while using the same CPU speeds respectively. I was surprised to see both RAM kits scored virtually the same benchmark score; yowsa. Increasing the HT speed had no affect on performance so I set that to 2000MHz, up from the stock 1800MHz of AM2 socket Phenom II 940s.
Most NB-links on AM2 motherboards are stable up to 2400MHz w/no over-volting required however this may vary. Most AM3 motherboards are stable up to 2600MHz w/no over-volting. If you're worried at first and have low motherboard temperatures, give them a 0.1v bump to ensure stability and turn it down later after you've tested stability just to see if you need that 0.1v bump.
/This guide may or may not be appended in the future. Hmm.
