According to ASUS, the "ASUS EPU utilizes innovative technology to digitally monitor and fine-tune the CPU power supply with improved VR responses in heavy or light loadings. Working together with AI Gear 3+, it automatically provides power for higher performance or improves efficiency by 50% when the PC is running low intensity applications - helping you attain the best possible power efficiency and energy savings of up to 80.23% to help save the environment".

In the next few pages or so, we will be sharing with you our findings on EPU. First and foremost, the EPU functionality is not enabled by default. EPU functionality is tied with ASUS AI Gear 3+ power management software. AI Gear 3+ is part of ASUS' AI Suite and the suite needs to be installed first before we can start playing with EPU.

The ASUS P5E3 Premium (Intel X48) features ASUS EPU.

Before we get started, here are the parts used for our test setup:

Test Setup 1

• Intel Core 2 Duo E4500 / Intel Core 2 Duo E8400 / Intel Core 2 Extreme QX9650
• Asus P5E3 Premium
• Aeneon 1333MHz DDR3 2GB kit
• Seagate Barracuda 7200.7 80GB SATA
• Zotac GeForce 8400 GS 256MB
• FSP Everest 80plus 600w PSU 

Test Setup 2

• Intel Core 2 Duo E8400 / Intel Core 2 Extreme QX9650
• Asus P5E3 Premium
• Aeneon 1333MHz DDR3 2GB kit
• Seagate Barracuda 7200.7 80GB SATA
• XFX GeForce 9800 GX2 1GB Black Edition
• FSP Everest 80plus 600w PSU 

Each AI Gear 3+ setting will result in the FSB (and multiplier) to be changed. Let's walk through each setting throughly and take a look at what happens.

The first processor we tested with the ASUS EPU is the Intel Core 2 Duo E4500. It is a 2.2GHz part with a 800MHz system bus, and 2MB of L2 cache.

There are five modes to choose from in AI Gear 3+: maximum power saving, medium power saving, high performance mode (normal), turbo and auto.

We first proceed to test the maximum power saving mode.

We note that the FSB is reduced to 180MHz from the default 200MHz. The multiplier goes down from the default 11x to 6x. If one were to just enable C1E/EIST via the BIOS and not use AI Gear 3+, the multiplier will also drop to 6x on idle. A lesser Vcore is used to power the processor at this stage.

However, interestingly, on this mode, the multiplier is locked to 6x irregardless of the processor's load level. As a result, the CPU only runs at 1080MHz on full load (180 x 6). Although this produces an impressive low power consumption on full processor loading (since processor speed and Vcore remain the same as idle), performance is effectively halved as we would see from the performance table shown later on in this article. 

The next mode is the medium power saving mode. The FSB is increased by 10MHz from the maximum power saving mode's 180MHz. The multiplier value still remains at 6x on idle, although the Vcore is increased a little.

On load, the multiplier behaves 'normally' by kicking up to 11x, which is the processor's default. On a system without AI Gear 3+ being in control, the multiplier will be 6x and 11x on idle and load respectively. Since the processor is now running at 2090MHz (190 x 11), a slightly higher Vcore is pumped in on load.

Maximum performance mode is reported as 'Normal' setting by AI Suite as well. The FSB runs at the processor's rated speed, and the multiplier behaves the same way as a system with C1E/EIST enabled.

Basically running a system with the high performance mode, is the same as running the system without ASUS AI Suite installed.

Turbo mode exhibits the same behaviour as the maximum performance mode, but the FSB is overclocked to 210MHz. At maximum processor load, the processor runs at 2310MHz (210 x 11). This means the processor is actually running overclocked. I would probably call it a 'mini-overclock' mode since it forces a higher than default FSB speed, yet retains C1E/EIST power saving behaviour by kicking down the multiplier to 6x on idle and going back up to 11x on load. In the subsequent tests in the following page, the processors are also similarly overclocked at about 5% without any compromise to stability.

Even though both processors are different physically - one is a dual core, and one is a quad core, they both run on a 1333MHz system bus (333MHz FSB). Our testing shows that the way AI Gear 3+ controls the FSB with either processor is the same.

In maximum performance saving mode, AI Gear 3+ drops the FSB to 300MHz. However, similar to our findings with the Core 2 Duo E4500, the multiplier is locked to 6x irregardless of CPU load, which is the multiplier activated when C1E/EIST kicks in.

E8400:

QX9650:

Switching to medium performance saving mode increases the FSB to 317MHz, but still below the default FSB of 333MHz. For this setting, the multiplier is not locked to 6x at all times. On load, the multiplier is set back to the processor default of 9x.

E8400:

QX9650:

High performance mode is essentially running without AI Gear 3+, but leaving C1E/EIST enabled in the BIOS.

E8400:

QX9650:

Turbo mode overclocks the FSB to 350MHz. This results in the processor being slightly overclocked as well on load. On idle, the multiplier drops to 6x and raises back up to 9x on load. This behavior is similar to the other modes with the exception of the maximum power saving mode where the multiplier is locked to 6x at all times.

E8400:

QX9650:

Let's take a look at some power consumption figures from the various processors.

As mentioned earlier in this article, on maximum power saving mode, the multiplier is locked to 6x irregardless of load level. Hence, as a result we have a processor running at only 1080MHz on full load. This is clearly reflected on the graph where power consumption on load is significantly lower than the other modes.

On auto mode, AI Gear 3+ opts for the maximum power saving mode on idle but turbo mode when the processor is loaded.

The same results are observed for the E8400 processor. There is comparatively less power is used on load when the maximum power saving mode is chosen.

Again, we note the same results for the Core 2 Extreme QX9650 processor. Interestingly, this processor is consuming lesser power at idle as compared to the Core 2 Duo E8400 processor across all modes even though it has four cores, two more than the latter.

To test performance impact caused by the different modes, we have decided to run a synthetic benchmark and two game benchmarks.

The synthetic benchmark was run on Test Setup 1, while the two game benchmarks were run on Test Setup 2.

First up is Cinebench 10 on Test Setup 1.

Turbo mode overclocks the FSB and indirectly causing a processor overclock as well, which results in better performance over the high performance mode.

In auto mode, AI Gear 3+ simply loads the turbo mode profile when there is loading. Performance scores end up the same as running AI Gear 3+ manually set to turbo mode.

As you can see, all three processors' performance are severely handicapped when the maximum power saving mode is used.

Next we decided to run Crysis and World in Conflict, two of the later released games which are very demanding on a PC. The Core 2 Duo E4500 was retired for these tests, so we have results only from the Core 2 Duo E8400 and the Core 2 Extreme QX9650.

E8400:

In maximum power saving mode, we get much reduced performance as compared the high performance and auto modes.

It becomes very evident in the World in Conflict test that the maximum power saving mode causes a drastic drop in performance. The processors are reined in at a measly 1800MHz, which is almost half of what they are actually rated to operate at.

QX9650:

Weirdly, we get a strange performance hit while running the quad-core in maximum saving mode. We tried repeating the test over reboots but the results remained the same.

Maximum saving mode conserves power, but it also reduces performance considerably.

For those who just need to check their email, or just check something, they could just use the built-in ASUS Express Gate feature found on ASUS' higher-end motherboards. By using Express Gate, you are ready to surf the Net in five seconds. This beats wasting a minute or so booting into Windows and then you wait again for Internet Explorer to load. Booting to Windows actually consumes quite a bit of power, so by using Express Gate, you skip the booting stage completely. This leads to power saved over the long run.

Express Gate contains a very basic version of the Linux OS, which is embedded on a tiny flash drive connected via USB found on the motherboard. Striped down versions of both Mozilla Firefox and Skype are included the embedded OS that appears right after you power on your computer. You can choose to boot into Windows (and waste time and power) , or simply enter the Linux OS and start surfing instantaneously. 

Kudos to Asus for making such a nifty and handy feature, as some of us are simply too lazy to wait for the computer to start up sometimes, just to check some of our favourite websites and email and/or communicate with friends, family or colleages. Express Gate grants you that ability to keep in touch - minus the hassle and power wastage.

Phases of power on the P5E3 Premium gets shut down whilst EPU is at work

Summary modes in AI Gear 3+

• Maximum power saving: Kicks both FSB and multiplier down. Multiplier does not raise back to processor default on load. Recommended for applications/usage where it is not processor-intensive.

• Medium power saving: Kicks both FSB (not as low as maximum power saving mode) and multiplier down. Multiplier raises back to processor default on load. Processor speed is still slower than its rated speed even at its default multiplier because the FSB is lowered. This mode can be used if the user is willing to sacrifice some performance for power savings. If you do processor intensive work, yet wish to save power, this mode could be for you.

• Maximum performance: The default AI Gear 3+ setting. System behaves the same way as with or without AI Gear 3+ installed.

• Turbo: FSB is overclocked. Multiplier is kicked down on idle, but raises back to processor default on load. This mode results in the processor being overclocked. Does not save power on load.

• Auto: AI Gear 3+ automatically picks a mode depending on computer usage. This mode actually uses the Turbo setting when the processor is loaded.

One important point to note is that ASUS AI Suite does not work if C1E and EIST are disabled. If you attempt to load the AI Suite software, the process would start and then freeze up.

Conclusion

For the average user, we would still recommend leaving AI Gear 3+ to high performance mode (if you have ASUS AI Suite installed), or just leave the C1E and EIST settings in the BIOS enabled for power saving whenever it is possible.

If you're an avid gamer who plays games from the moment you power on the computer and you choose Auto mode, no doubt you get a performance boost from the slight overclocking, it also results in your system consuming more power. If you just use your computer to surf the Net, play music, then you would benefit by setting AI Gear 3+ to maximum performance saving mode. The processor runs at a lowered speed with less voltage since FSB is lowered and the multiplier is also lowered and locked. Surfing the Net does not require much processing power at all, so one would not notice any loss in performance under such circumstances.

The ASUS Energy Processing Unit is nevertheless an interesting development by ASUS. The EPU does help to conserve power on Auto mode when your PC in on idle only, and unless you're well-aware of your usage patterns and what your applications require, and choose the most suitable mode according to situations, you might just end up consuming more power than necessary instead, albeit with enhanced performance (with the slight overclocking) without compromising stability (We've got Rock Solid, Heart Touching remember? ;))

We've briefly heard about the second rendition of the EPU which promises better power management and with MSI and Gigabyte also in the race to save more trees, we can only wait and see which company comes up with a better tree-saving mechanism with the help of their lovely Voltera and Intersil counterparts. =)