Phenom II AM3 Overclocking Essentials
-A guide I wrote on essentials when OCing those Phenom II’s

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Introduction

Ever wondered why you can’t get past 3.6GHz on that new Phenom II? Some may claim it is a bad chip, but I for one, can guarantee you that is almost always not the case.

I have been overclocking this chip for weeks and studying how it acts while doing so. I may not be an AMD engineer, or an electrical engineer, but here is what I have found:

1) Voltage

People always repeat the same/similar phrases about these chips “Up the voltage, AMD chips are tanks and can take it!” In fact, I have found with the new AM3 Phenom II’s that it is not always practical to up the voltage past 1.5Vcore if you are just looking for a 24/7 overclock. Before upping Vcore, take into account what else may be causing stability. It could be an unstable NB (IMC) or Ram. I suggest finding the max stable ram and NB clock before OCing the CPU cores.

Also, you may run into your system not booting with more than ~1.475vcore. This is because these new Phenom II’s actually dislike and do not tolerate high voltages a lot of the time. You are lucky to gain a chip with high leakage, so that you can sustain stability with 1.55V+

A common misconception is that these 45nm Phenom II’s are using dangerous amounts of voltage for anything past 1.4Vcore. Comon people, these aren’t 45nm Core 2′s or Core i7 CPUs. AMD’s 45nm process is completely different, and can maintain higher voltages without any traces of degradation. However, I do not suggest going over 1.55Vcore for a 24/7 air OC.

Last but not least, remember that voltage adds heat to these chips, of which they do not like under high clockspeeds.

2) Heat

The max heat these chips can tolerate without risking damage is 62C. However, instability and crashes can be caused all the way back into the 50-55C range.

Through experience, I, and many others have noticed that these chips LOVE cold. In fact, they scale way better with cold temperatures than adding more voltage to the mix. A great example of this can be seen with some Dry Ice results on these chips:

Heres another example of the scaling with cold. This was done with only -8C temperatures and chilled water (Corsair H50):

Take a good hard look at those overclocks. 4.6GHz with only 1.408vcore, and 5GHz+ on chilled water?. Simply amazing. Now do you see why temperatures play such an important role? (Note the second result did use a higher voltage, but it had the temperature to compensate. On air cooling, temperature is still more important than voltages).

If you plan on air cooling, pick up some nice high CFM fans (as long as you can stand the sound) and a nice heatsink cooler such as the Xigmatek S1283 or a Thermalright Ultra Extreme 120. Other recommendations: Thermalright Venomous X-RT w/ pushpull config, corsair H60,80. If your chip is a six core (1090T or 1100T) the latter is a better recommendation.

IMPORTANT: When using programs such as Core Temp with a Phenom II X6 (Thuban) CPU, the temperatures are reported 10-13C below what they are in actuality. Make sure to set a delta if this is the case! Other programs report correctly, but this is my experience with Core Temp.

3) Multiplier Overclocking

If you are like me, and have a Black Edition cpu, you have probably figured out that overclocking is a piece of cake by just flicking up the multiplier and being done with it. This is not always the case.

I personally recommend against just using the multiplier. Many people have found that using a lower multiplier and a higher HT Ref. Clock can help increase your max overclock+stability slightly.

Not only that, but only using the multiplier will not always net you the best performance. Sure you can hit 4GHz with a 20X multiplier, and a bit more voltage. However, through benchmarking or game performance, you may find it is performing worse than someone else’s comparable 4GHz using a higher HT Ref Clock. This is because when you up the HT Ref Clock, it also increases ram speed, HT link speed, and NB (IMC) speed. Just remember to watch the stability on each of these.

4) Troubleshooting/Stability:

Here is a direct quote from our very own Chew*:

“Im sure some of you may have experienced a crash with cinebench………sometime you will blue screen, somtimes you will just black screen and sometimes the bench will just crash ( dissapear, etc just shut down ) and windows will still be up………..the blue screen is NB vid/IMC memory related, the black screen is core clocks/cpu voltage related and the just crash/dissapear from desktop is temp related………….”

Next time you experience a crash, take a good hard look at that for reference. Chew* has more experience than I with these chips, and honestly, he is right about the crashes. I checked myself.

The best method of finding stability on your overclocks is to use Prime 95. Now it is usually debatable for how long you should run a program like this. For the Phenom II’s however, you need to wait all the way until you can be sure the IMC (NB) is stable. The NB is stressed the most during 512K FFTs. This happens about 2-3 hours into Blend, so I suggest running for at least 3 hours.

Here are a few fixes to common problems:

4GHz stable is not easy with these chips (mostly the quadcore Phenom II’s). In order to achieve 4GHz 100% stable, you need 32-bit windows and you will have to back off memory and NB clocks (maybe even going below stock). However, it would net you greater performance with a 3.8GHz and 2600-2800MHz NB.

Post C3 Update: The above paragraph only applies to C2 / old revisions of Phenom II. Most Phenom II’s can hit 4GHz+ with good air/water cooling on 64-bit versions of windows as well. Also the IMC has changed in newer revisions so 3000MHz NB is attainable with around 1.3250 CPU_NB voltage. Keep this in mind if you purchased your Phenom II C3 after the release of the 1090T (April 2010). As well, it is easier to clock up ram on easier IMC’s (2000MHz is attainable on thuban’s IMC). Here is a list of changes I compiled when C3 released: http://slappablog.wordpress.com/2009/11/06/phenom-ii-c3-revision-changes/

If experiencing memory instability, try upping the NB voltage (not CPU-NB VID).

If experiencing overall instability, first check to make sure ram is in check at stock speeds. If that is not the case, try giving the CPU-NB VID +.100 or +.200v.

Remember instability does not always come from the cpu cores! It can be the NB or ram causing crashes!

As a last resort, make sure you have the newest BIOS!

5) Core Balance

Some people think that because one (or a select few) of their chip’s cores are holding them back, they can be downclocked while the others are overclocked. Please keep in mind that doing so will cause a load imbalance on multi-threaded programs and will actually slow down your performance as opposed to speeding it up. The only time when this is acceptable is suicide overclocking or running single threaded apps on the overclocked core in particular.

6) Motherboards & Power Phases

The release of the Phenom II X6 CPU’s (thuban) has added more variables into play when overclocking. Keep in mind that is strongly recommended that you have a motherboard with 8+2 Power Phases, with the VRM’s covered by a heatsink. This allows for better stability, and cleaner power delivery. You can still overclock the X6 on motherboards with 4+1 Phases, but I strongly recommend to avoid pushing these platforms too hard (mostly the mATX boards 880G, 870, 780, 890GX) boards. There have been a lot of dead boards/ chips from doing so.

Read more about it here.

7) Tweak!

Honestly, I mean it. Mess around with as many settings (even if you think they won’t change anything) as you can. Every setup is different so experimenting won’t hurt. There is still more to be discovered about these chips!

And this concludes my basic Phenom II AM3 Overclocking Essentials Guide. Hope this will prove a useful reference in the future!

For Phenom II Ram and Northbridge Overclocking, please check out my second guide here: http://slappablog.wordpress.com/2010/10/14/phenom-ii-imc-ram-overclocking-guide/