Today, we are going to talk about the Application Power Management (APM Master Mode) and HPC Mode (High Performance Computing) BIOS settings that are available on many AMD Motherboards using Socket AM3+ CPU's. It seems there is a lot of misinformation on the web concerning exactly what these settings mean, and how they effect your CPU, especially in overclocking situations. In this post, we will explore what these settings mean, what effect they have, and if you should enable or disable them.
So without further delay, lets get started.
AMD Application Power Management (APM Master Mode) -According to AMD, Application Power Management is a technology inside your AMD FX CPU that works in conjunction with AMD Turbo Core technology that will allow your CPU to reach Turbo Core speeds (running above base clock speed) as long as there is thermal and voltage headroom available.
Take the FX 8150 as an example, it has a base clock of 3.6 GHz. It can Turbo Boost to 3.9 GHz when up to 8 cores are active, and Boost up to 4.2 GHz when 4 cores or less are active, As long as there is thermal and voltage headroom available to do so. If the CPU is under heavy load and there is no headroom available, the CPU will run at its base clock rate of 3.6 GHz.
Now notice the part I underlined above. What is Thermal and Voltage headroom? This refers to the CPU's TDP(Thermal Design Power). the definition of TDP is the max amount of heat generated by the CPU that the cooling system is required to dissipate under operation. Voltage and clock rate play a big role in maintaining such a TDP. APM also ensures your not putting to much stress on your motherboards VRM and power phases which most times don't have the cooling solutions or active fans like your CPU does. In my FX 8320 undervolting guide, I show you how lowering CPU vcore can make a significant impact on CPU temperatures, especially under load.
In a nutshell, AMD Application Power Management BIOS setting ensures the CPU stays within the 125W (8 core) or 95W (4 and 6 core) TDP the chip was designed for. I have seen many say that APM causes the CPU to throttle, this is both true and false. It is true that sometimes APM causes this, but throttling is not what it always does. there are times where it will slightly lower voltage while keeping the CPU at a higher clock rate.
HPC Mode (High Performance Computing) - HPC Mode is a setting in the BIOS that prevents the CPU from lowering and locking its clock rate under load in certain conditions. In some benchmarks, HPC Mode can increase performance by about 6%, but these performance improvements are only realized in benchmarks like HPL. Dell tested this setting for the AMD Interlagos Server based CPU's and saw very little performance increase outside of HPL benchmarks. HPC Mode did however increase power consumption and power draw for very little benefit.
In a nutshell, HPC Mode prevents the CPU from locking and lowering its clock rate when the chip is either getting close to going over the TDP, or the motherboard CPU socket temp is getting to high. This is not always true in all cases though, because in certain situations, the CPU can still drop and lock its clock rate under load. This setting is more geared to very specific environments such as clustered computing where there are specific applications running that would benefit from this setting. Those situations are not your average home user.
Should I enable or disable Application Power Management and HPC?
As an overclocker myself, I would say No. Do not disable Application Power Management, and don;t enable HPC Mode.
All disabling APM does really is cause your CPU to run outside the 125w TDP range. In essence, your drawing more power and voltage, and creating more heat for very little benefit. The same goes for HPC Mode. Unless your running some cluster server with very specific applications, enabling HPC mode is just going to generate more heat and power draw for very little benefit.
I can say 99% of CPU throttling problems on FX CPU's are due to either buggy BIOS in need of an update, or the more commonVRM throttling. Your motherboard will throttle the CPU if the VRM phases get to hot or outside of a safe zone coded in the BIOS. This is hard-coded in and set to help prevent frying your motherboard.
This is most common on the AMD 970 chipsets and the lower end boards that have 4+1 power phase designs. These are not high end power phase designs, and even an FX CPU at stock will throttle on these boards. Moving up to a 990FX board with a 6+2 or greater power phase design and good beefy heatsinks on the VRM and chipset will result in throttling problems going away without even having to change or mess with those BIOS settings.
In my experience, on an Asus M5A99FX Pro Rev 2.0 board, enabling and disabling APM and HPC Mode had no discernible effect whatsoever in any of the applications or games I run. I was still able to push 60 FPS solid in Crossfire on games such as Skyrim, Devil May Cry, Tomb Raider, and other titles with APM enabled and HPC Mode disabled. the only difference I saw between APM disable and HPC Enabled was higher core temps, high socket temps, and more power draw. The performance of the games and applications was identical.
The throttling many say these CPU's do, on the right motherboard with a 6+2 phase design or better, without buggy BIOS's are merely cosmetic. The FX 8350 dropping to 2.9 GHz for 1 millisecond or less before jumping back up to 4.2 GHz Turbo in game will not be noticeable whatsoever, as these drops are algorithm based to do so when the CPU has room to do so. There is more too these settings then just throttling, sometimes, it may just slightly drop Vcore while maintaining base clock rate to lower heat and keep the TDP profile, othertimes, it will boost voltage and multiplier to give you a boost.
The only time and situations I would recommend Disabling APM(Application Power Management), and enabling HPC Mode is if you have:
1. A very good preferably high end liquid cooling solution for your CPU for planned high overclocks in the 4.9 to 5GHz range that would go over the TDP limit anyways.
2. You have custom heat sinks and active fans on your motherboard's VRM, Northbridge, and other chips on your motherboard.
If your not overclocking that high and don't have the active cooling for your motherboard, I would err on the side of caution against it. If your having throttling issues, they are more then likely related to motherboard VRM throttling or buggy BIOS. In these cases, either invest in a better motherboard, or see if you can get your motherboard manufacturer to update the BIOS to fix the issue.
I hope this answered your questions, and as always, comments are always welcome!
Image By User:Pepetps (Own work) [Public domain], via Wikimedia Commons
Disclaimer: I am not responsible for anything that may happen to your PC when changing settings or changing registry values. If you choose to make changes, you do so at your own risk.. You are solely responsible for any damage to your computer , data, or other hardware due to user error, inadequate cooling, too high of voltages, incorrect software settings, and any other factors. Please remember to back up your computer before attempting this. If overclocking, Do not Overclock on the stock AMD or Intel CPU Heatsink and fans. Use Aftermarket cooling heat sinks of sufficient TDP or water cooling to ensure best chance of not having premature hardware failure. As always, remember to backup your data before attempting any change. I am not responsible for data loss or damage of any kind.