This post is not meant to be universally right, it just sums up my personal experiences and may provide a couple of grappling hooks to people who have trouble.
Always use the latest AMD OverDrive. The latest version is v.3.0.2.
This post is very basic and covers everything regardless of many people knowing most of it by heart.
Let's start with the history side. Yesterday (at the time of posting this) my new CPU arrived, which is a Phenom X4 9550, replacing the older Athlon64 X2 4000+. Bought it for approximately 185 dollars plus shipping (Europe).
The old processor ran at 2.93 GHz, and did that between 1.500 and 1.525 volts, thanks to unlucky binning. The new processor ran at 2.2 GHz. I know benchmarks, I knew single- or double-threaded performance would suffer. It is basically why I decided to overclock and find the maximum.
The following are my observations and are by no means universal laws or such.
What to note:
AMD's Phenom is the same monolith to CPUs as what nVidia's G80 and GT200 are to GPUs. Similarly, it has 3 main domains to check on and overclock/restrict:
CPU multiplier, memory controller multiplier and HT multiplier. Also, I'll be noting some things regarding RAM, as I had issues there too, at first.
1. CPU multiplier
- Advantage: allows boosting processor speed without taking on the RAM as well, ergo multiplier-overclocking requires no checking on the RAM afterwards.
- Disadvantage: the increments are coarse, even with half-multipliers.
- Other: some cores may be performing sub-par to others (people frequently complain about the third core, a.k.a. #2) - by setting the multiplier lower, you can achieve a stable boot, then use AMD OverDrive's automatic profile loading to bring the remaining 3 cores to the maximum multiplier once Windows has started.
2. Memory Controller multiplier
- This specifies the speed at which the CPU's memory controller will work, and is rarely likely to function happily above 2100 MHz (or even at just that much). I haven't tried it actually, I know my PC doesn't boot with 2300 MHz and works just fine at 2080, so my estimates may not be true. Note that AMD OverDrive will report this speed as "Northbridge (NB) speed".
- You should decrease this multiplier if you have to push the reference clock (like in my case - I didn't get a Black Edition processor). As I stated, the system is likely to become unbootable if you keep it high. Although 9 may be workable for mild overclocks and 8 seems like a sweet spot, you may need to throttle back to a multiplier of 7 if you push the reference clock far too high.
- Other: note that this multiplier has no effect at all on the speed of your RAM sticks, but has an effect on system performance.
3. HT multiplier
- Now this one is a total bitch. I've had more "take out battery, wait, place it back" cycles because of it than ever before (might've been the board's fault at the time, too). The deal is basically this: your HyperTransport link provides the main interconnect between your CPU and your motherboard (at the northbridge). The BIOS isn't letting on more than that, although I've heard it's also the inter-core connection. While its multiplier may vary from 1 to 13 (in my PC), which means 200 to 2600 MHz using the default reference clock, a Phenom (or newer) system will be constantly throttling back whenever the HT link reaches or outruns the memory controller's speed.
- That means you need to keep the HT multiplier equal to or less than the memory controller multiplier if you plan to overclock at all. Apart from the down-throttling deal with PCs, I've also noticed utter unbootability (with a higher reference clock) if my HT multiplier exceeded the memory controller's by 1, 2 or more, even if I was attempting to keep its actual speed under the absolute limit of 2600 MHz.
Basically, you want to achieve the highest possible multiplier+reference clock configuration, while keeping the memory controller at bay (relatively), and checking the HT link according to the memory controller. This isn't the case where you want everything maxed out, but it might not matter at all anyway, so long as the CPU speed is high(er).
Here comes the other nuisance, pure candyland:
Phenom RAM controlling
Phenom processors can work with RAM in "Ganged" or "Unganged" mode. This setting might have a bigger impact on your system's overclockability and/or performance than you think. Note that both settings are "dual channel" regardless of the physical bit width numbers your motherboard will post.
* Ganged:
Your RAM modules are "ganged" together and one core handles full dual-channel. This is optimal when you're testing with synthetic benchmarks: Sandra and EVEREST are not compatible with Phenom's RAM methods and only recognize single-threaded memory handling. Therefore, ganged mode is for getting the kicks out of benchmarks.
Note: your RAM will be more stable.
* Unganged:
Each RAM module you have can be paged at any time, thanks to "multithreaded memory handling". This is the option you want if you don't play benchmarks. It will provide the best performance, and it will show in numbers too, once Sandra and/or EVEREST receive updates accordingly.
Note: some motherboards have shoddy support, where you might need to raise voltages even at stock speeds because of this - if it works at all. On a good board, this setting should work fine.
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That's all the info about it, here's the basic "to do list":
- Increase multiplier or reference clock until it becomes unstable (BSODs are often caused by CPU errors, so you'll know it's that). Then increase voltage, rinse and repeat.
- Every now and then, make sure that your memory controller isn't running too fast. Trying to keep it to/under 2100 MHz may be a good target.
- Always restrict the HT multiplier to the memory controller multiplier.
- Set your memory speed one notch lower (for example, 667 MHz DDR2 for 800 MHz modules), but make sure your timings don't tighten along with it. You will know that RAM instability is occuring, if your computer reboots out of the blue or if the screen freezes - milder faults might cause programs, services or drivers to stop, or DEP to malfunction.
Some RAM kits come with varying SPD values, even from the same brand and type. Try setting timings to the lowest common denominator to reach that extra notch with the system, should RAM hold you back.
* When you have the maximum CPU speed, you can experiment with higher memory speeds, unganged mode, timings/voltage and whatever else floats your boat.
Note: your motherboard northbridge and southbridge may require a tiny voltage bump, just in case.
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I hope some of the above information will help those who want to overclock Phenoms but are stuck or experience disappointing limitations and results.
I might update this space if I get even higher results from my CPU (currently 2,926 MHz). Stay tuned. I hope I'm not a victim of **** binning again. But I surely am, I know my luck.
Version 1.2 p.s.: I might update this if I get that motherboard I was eyeing with working ACC. That should send off system performance further with a horse kick.
