Phenom II IMC & Ram Overclocking Guide


Over the recent months I have watched and observed as the Phenom II CPU found its niche within various enthusiast communities and online forums. Users have been provided with an excellent, all around, 45nm AMD quadcore.

However, there is one factor that people still find confusing and unclear. Overclocking the Phenom II. Why are people so confused?  One reason may be because they add a lot of new variables and overclock differently than the competitors chip. Some may choose to see Phenom II overclocking as a headache, or a fresh challenge in their hands. I choose to see it as a fun challenge.

Now, one area that people have mass amounts of problems is Ram/Memory stability and overclocking, as well as what role the IMC (NB) plays in affecting ram and performance.


The IMC links the CPU to the memory in a system. In the case of the Phenom II AM3 series, DDR2 or DDR3 memory is supported. One important performance factor that people neglect when applying daily overclocks to their Phenom II systems is that the faster the IMC speed is, the better your memory will perform. Additionally, you have to take into account that overclocking the IMC may require voltage increases on the CPU/NB. This may add unwanted heat which happens to be the Phenom II’s arch-enemy. While overclocking though, always keep in mind that the IMC is a very touchy factor in an overclock. If it’s not working out for you, you perhaps need to try different combinations/ratios. When stress-testing the IMC, the most preferable method is Prime 95 blend test for at least 2-3 hours.

The Ram

The memory within an AM2+ or AM3 configuration acts and requires different tuning than your average Intel setup. The RAM ties strongly in with the IMC. If the ram is unstable it can cause instabilities in the IMC and vice versa. Ram on this platform tends to like lower memory frequencies and timings. When tuning ram, take into account every setting you can find in your BIOS. I mean it. Experiment. It may seem like a lot to take in, but hey, grab a coffee, a pad of paper, and sit down for 2 hours and do some testing. The second important portion of RAM clocking is that you must know what type of IC’s your RAM uses. This already will put you in a great position to fine tune the ram. Plenty of online resources can help you identify your IC’s if you do not already know. Once again, after clocking your ram, 100% stability can be found using Prime 95 linked above. Stability testing for benchmarking overclocks can be done in SuperPi 32M.

The CPU Cores

Since the focus of this article is geared towards Ram and IMC clocking, I will be quick on my CPU Cores description.

Phenom II CPUs are usually very intolerant to high voltages when using air setups. Be aware that more voltage may decrease stability going past 1.5V on quad core versions of Phenom II. Also remember that these cores love cold temperatures and scale brilliantly with it. This can be seen in my Canadian Winter blog series, as I will soon start to compare the scaling from normal air temperatures to very cold air temperatures. Even without winter air, every degree that you can lower your temperatures in an air setup is worth it towards overclocking.

Pulling It Together

This creates a 3 component chain wherein lies the secret to stability and performance. You have to realize that if any component in this chain (CPU, NB, Ram) happens to be unstable, the chain will not be complete and you will never see stability. In order to maintain stability, you have to find a sweet spot for each variable according to your setup. There are a plethora of ways you can approach this. However, I discovered that some specific methods are more efficient than others.

The Overclocking – Guide

Starting With The RAM

It is unarguable that even out of the box, with bare bone stock settings in a BIOS, memory will cause the most headaches for the AM3 setup. For example, prior to Phenom II X6 chips which include a brand new IMC revision, you could not take a standard 1800MHz 9-9-9-24 set of DDR3 and get it to run at it’s rated speeds without doing some tweaking to settings in the BIOS . Even sticks that can in fact run at rated speeds out of the box on an AM3 platform can be a pita for stability. This is in contrast to the CPU and IMC where on stock settings, they are supposed to operate flawlessly without any rifts.

1) To begin your overclock start with a default ram clock and timings. For example: 1333MHz 6-8-6-24. This can also depend on the stock specs of your ram to begin with. That is always a good starting point (excluding stock 1800MHz and 2000MHz sticks, as it is unlikely you will get them to run properly at first starting at such a high frequency).

2) You can start speeding up your ram in a variety of ways. By increasing clock speed (Through dividers and HT Ref Clock), tightening timings (adjusting latency timings, and sub-timings in the BIOS), or combining both for the ultimate overclock. Start in small increments on the frequency and timings. Remember that the 4 major ram timings (CAS, tRCD,tRP, tRAS) are very dependent on what IC’s your ram has, and changing these more then one value at a time can cause instant instabilities requiring a CMOS reset. Also remember that it is contradictory to loosen all timings significantly to increase frequency and vice versa. What increase in speed will there be if you are just trading off one thing for the other? However fiddling around with some sub-timings and loosening can help stabilize higher frequency overclocks, while minimally affecting performance. Generally, the most important part of ram clocking is getting familiar with your ram, and what settings greatly affect performance and stability. This is a lengthy process and there is a lot of rebooting involved. General ranges to shoot for would be: 1333MHz (CL 5 or 6), 1600MHz (CL 6 or 7), 1800MHz (CL 6-8), and 2000MHz (CL 7+). What range you want to fall into also depends on your ram, the quality of the IC’s and your ability to tune the timings. Remember to always experiment as much as you can and play around with everything available!

Here are a few sources that list different DDR3 IC’s:

3) With each small change you make it is important to know if you are stable or not. In windows you can use Super Pi 32m as a preliminary stability test. This will not gauge 100% stability, but it will help you figure out what range you will be able to overclock within. Passing 32m also means that you are stable for most benchmarks. If you cannot pass 32m, then your ram is not remotely stable, and you can then adjust your settings accordingly. For full stability testing for 24/7 overclocks, utilize Prime 95 for at least 3 hours. During any stability test, it is important to eliminate the risk of cpu cores and IMC (NB Frequency) causing any stability problems. This is to ensure that if there are instabilities, they are occurring within your ram, not within your processor cores or memory controller. So make sure that the NB and CPU are as close as possible to stock settings prior to testing. Another thing to note: the more ram slots you have occupied with modules, the more stress it places on the IMC. This can make it harder to overclock/stabilize.

4) If you do find instabilities in your overclock there are a few things you can do to help stabilize them. First things first. Do not go crazy with the ram voltage. In moderation though, it can help. Recent DDR3 modules cannot take too much voltage on standard cooling. It is common for a lot of ram to come stock at 1.65v. Usually this ram should not exceed 1.75v for risk of degradation or damage to the ram. However some IC’s are known to like voltage more then others. Micron D9′s come stock at 1.8v usually and love voltage. Now that that’s out of the way, here are a few tips for stabilization. Increasing the CPU-NB voltage slightly is always helpful, regardless of whether the NB Frequency is at stock. NB Voltage is a setting in the BIOS that refers to the physical northbridge on the motherboard. Do not confuse this with the IMC. In some cases, increasing this voltage in moderation can help stabilize high ram overclocks. Another tip is to ensure that both of your ram sticks are in slots 3&4. On some Gigabyte 890FX boards these slots offer higher headroom for ram speeds. Keep the ram cool, pointing an extra fan toward it can always help. The final tip is to adjust drive strengths, which I will talk about in depth in the next step.

5) In the BIOS, there is an advanced set of ram settings. These are called drive strengths. Essentially you can use these to stabilize the ram further. It is very hard to understand which changes in drive strength values are useful unless you utilize memtest. You need to boot from this program off a CD or USB before going into windows. When changing the value of a drive strength always remember to do it for both sticks of ram (sometimes labeled DCT0&DCT1, or A&B). Only changing one value at a time, run a round of tests in memtest. You want to change drive strengths until memtest gives you as little errors as possible on the test suite. Once done so, you have essentially helped stabilize the ram or have created more headroom for overclocking. Remember that you cannot do this if you are getting preliminary tests of hundreds or thousands of errors in memtest. You need to begin with a handful of errors, and this is what you must use as your baseline value that you will start tuning from.

Adding In The Northbridge Overclock (IMC)

Once you have a proven ram overclock that is stable, it is time to work on the IMC. The IMC can vastly increase performance of the memory subsystem in all aspects. It allows a memory overclock to work to its full potential. Overclocking the memory controller is very similar to overclocking the CPU cores. It is much easier to overclock and understand then ram overclocking, as there are less variables in play.

1) When overclocking the IMC you need to know what will affect it’s  headroom. On the Phenom II X4, X3 and X2 chips, the NB Frequency has a max stable range of 2600-3000MHz depending on your chip. For 24/7 overclocks this frequency usually falls around ~2700MHz. This will require voltage increases in the CPU-NB option in the BIOS.  However, Phenom II X6 chips are slightly different. Their max 24/7 range is around 2800MHz-3000MHz. They also require less voltage then previous chips.

2) Start by increasing the NB multiplier till you hit around 2300MHz-2500MHz. Try stability testing this in Prime 95 combined with your ram overclock. Do not adjust the voltage to the IMC just yet. If this passes, then move up a notch. Go until the IMC causes Prime 95 to crash, and then start increasing voltage in moderate increments on the CPU-NB option. When overclocking take into account that the HT Ref Clock (which also controls your ram and cpu frequency) will become the base that is multiplied by the NB multiplier to get your NB frequency. This means that each multi increase will have a bigger increment as opposed to if the HT Ref Clock was left at 200.

3) For CPU-NB voltages, do not exceed 1.5v. After that the IMC won’t really scale well. Also note that each time you add voltage to the CPU-NB, you are adding to the overall heat output of the chip. So this is something to watch under air cooling, as it could hinder your CPU core overclock that you will later add in. The rule of keeping the chip cool also applies to the NB. A cooler chip could equal a higher overclock headroom.

4) When stability testing your final NB overclock, run Prime 95 for at least 3 hours on the blend setting. This is to ensure that the ram and NB are both stressed to the maximum during the 512K FFT iterations. You may wish to run this longer then 3 hours if you like, but that is more stress then any real-world application can offer. After this is stable, then you have yourself a final overclock of the IMC and Ram.

The Final Step

For the final step, you would add in your CPU core overclock. A great guide to check out for overclocking the CPU is my previous guide here. All this information should help in completing your final stable, 24/7 overclock. Here’s an example (it was only 2 hours because of time constraints):

I hope you guys enjoyed my second guide, stay tuned for more in the future.

About these ads