Windows Vista : Make Your Hardware Perform (part 3) - Improve Battery Life, Manage IRQ Priority

7/30/2012 5:56:07 PM

3. Improve Battery Life

Priorities shift when you're not tethered to an AC outlet. Suddenly, processor speed and the glitzy Glass interface just aren't that important when your laptop battery is going to die in 12 minutes. Now, there are things you can do to reduce your laptop's hunger for power, but the best power-saving features are the ones that engage automatically when you're using the battery, but revert to their high-performance settings whenever you plug in.

Start with the obvious: the Power Options page in Control Panel. Here, you'll find at least three plans: Balanced (the default), Power saver, and High performance. It doesn't really matter which one you choose, because each can be configured any way you like.

Click the Change plan settings link under the currently selected plan. Next, click the Change advanced power settings link to open the Advanced Settings window, and if it's there, click the Change settings that are currently unavailable link .

The settings here that will have the most bearing on your battery life are:

Hard disk

Being a mechanical device, your hard disk eats up a lot of power. Set the Turn off hard disk after option too low, and you'll spend a lot of time waiting for Windows to wake up your hard disk; set it too high, and you're just wasting power. A setting of 10 or 20 minutes is usually a good compromise.

Processor power management

Your processor can run at different speeds; it runs fast when it's needed, but drops down to a slower speed when your PC is idle. The two settings here let you choose the upper and lower bounds of your processor's speed. Unlike with your hard disk, you never have to wait for your processor to be woken up, so there's very little cost in keeping the Minimum processor state setting as low as possible.

It's worth noting that the Maximum processor state is set to only 50% in the Power saver plan by default; this means that when this plan is active, your CPU will never run faster than about half its rated speed. Of course, this does save power, but as long as the Minimum processor state is set to, say, 5%, you probably won't need to limit your CPU in this way. Of course, processors vary, so experiment with this setting to see how well yours manages its own power consumption.

Search and Indexing

Windows indexes the files on your PC to make searches faster. Of course, this uses your hard disk heavily, so it's best to set the Power Savings Mode to Power Saver when you're running on a battery.


Use the Turn off display after setting as a battery-friendly alternative to a screensaver. Since it takes very little time to wake up modern laptop displays, set this to a small value like 5 minutes. Then set Adaptive display to On to have Vista automatically (and temporarily) give you a little more time whenever you seem to be frequently waking up your display.

Click OK when you're done; the changes take effect immediately.

To switch between power plans, just click the battery status icon in your notification area (tray) and then click the one you want. Or, press Winkey+X to show the Windows Mobility Center, where you can also choose the plan you want.

3.1. Switch plans automatically

Problem is, you have to switch power plans by hand, and who remembers to do that? Wouldn't it be better to have the plan chosen automatically when you switch between battery and AC power? Vista won't do this, but the free Vista Battery Saver (available at, and shown in Figure 4) can.

Figure 4. Tired of having to change the power plans every time you switch between AC and battery power? Increase your battery life by letting the Vista Battery Saver do it for you

Vista Battery Saver can also turn off the power-hungry Glass interface when you switch battery power, a convenience that has been known to cause huge gains in battery life. Also available is Aerofoil (free from, a program that simply switches off Glass when you're mobile and then turns it back on when you've plugged in.

What's funny about all this is that in some of Vista's beta-test versions, each entry in the Power Options-Advanced Settings window had two settings: one for On battery and the other for Plugged in. Microsoft actually removed these settings from the final version, but if you have the Vista Business or Ultimate edition, you can still use them by opening the Group Policy Object Editor (gpedit.msc), and expanding the branches to Computer Configuration → Administrative Templates → System → Power Management. As it turns out, Vista Battery Saver is much easier to use, but if you don't want to install any third-party software, the Group Policy Object Editor is a workable alternative.
3.2. Disable devices, stop services

Don't need that ethernet port right now? Not using your DVD drive? Turn 'em off and save some more power.

Open Device Manager, expand the branches to show your "expendable" devices, and then right-click each one and select Properties. Choose the Power Management tab, turn on the Allow the computer to turn off this device to save power option, and click OK. Then, assuming the option was available, right-click the device and select Disable (if the option wasn't available, disabling the device won't save any power).

Next, open the Services window (services.msc), and stop any unnecessary services (don't touch the ones you don't understand). For instance, if you've installed Apple's iTunes on your PC, you'll see at least two related services here: Apple Mobile Device and iPod Service. If you have no plans to connect an iPod during the next few hours, right-click each service and select Stop to give your PC one less thing to do while you're running on precious battery power.

3.3. Cooler or hotter to save power

One of the most significant things you can do to increase battery life is to take your laptop off your lap. Put it on a book, magazine, airline tray table, tennis racket, pasta strainer, or any hard—and preferably ventilated—surface. If the bottom of your laptop is allowed to breathe, it won't get so hot, and the fan won't have to work so hard to keep the processor cool. The harder your fan works—and for that matter, the hotter your CPU gets—the more power is drained from your battery.

If your laptop never seems to get that hot, even when it's on your lap, you may be able to experiment with some more lenient cooling settings. Using your PC's BIOS setup page or, optionally, a fan control program like I8kfanGUI , try increasing the allowed temperature of your CPU by a degree or two, and see what happens. With luck, your fan should come on less often and your battery should last a little longer, all without (hopefully) frying your processor.

4. Manage IRQ Priority

Most components directly attached to your motherboard—including PCI slots, IDE controllers, serial ports, the keyboard port, and even your motherboard's CMOS—have individual IRQs assigned to them. An interrupt request line, or IRQ, is a numbered hardware line over which a device can interrupt the normal flow of data to the processor, allowing the device to function.

Vista lets you prioritize one or more IRQs (which translate to one or more hardware devices), potentially improving the performance of those devices:

  1. Start by opening the System Information utility (msinfo32.exe), and navigating to System Summary\Hardware Resources\IRQs to view the IRQs in use on your system, and the devices using them.

  2. Next, open the Registry Editor , and navigate to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\PriorityControl.

  3. Create a new DWORD value in this key, and call it IRQ#Priority, where # is the IRQ of the device you wish to prioritize (e.g., IRQ13Priority for IRQ 13, which is your numeric processor).

  4. Double-click the new value, and enter a number for its priority. Enter 1 for top priority, 2 for second, and so on. Make sure not to enter the same priority number for two entries, and keep it simple by experimenting with only one or two values at first.

  5. Close the Registry Editor and reboot your computer when you're done.

Some users have gotten good results prioritizing IRQ 8 (for the system CMOS) and the IRQ corresponding to the video card (found in the first step).

5. Overclock Your Processor

The processor (CPU) is the highest-profile component in your PC, and indeed, it does a lot of the heavy lifting in it. But processors also become obsolete the fastest, and given how expensive they can be, it's not always a wise place to put your money. That's where overclocking comes in; rather than spending money on a slightly faster chip, you can simply change settings in your PC to squeeze a little extra speed out of the one you currently have. (See the upcoming sidebar, "How Much the CPU Matters," for a little perspective.)

Overclocking is the process of instructing your processor to run at a higher clock speed (MHz) than its rated speed. For example, you may be able to modestly overclock a 2.40 GHz chip to run at 2.48 MHz, or your motherboard may offer overclocking at up to 30% of the rated speed, which would give you more than 3 Ghz on that same old chip.

Supposedly, Intel and other chip makers have taken steps to prevent overclocking (theoretically prompting purchases of faster CPUs instead), but some motherboard manufacturers have found ways to do it anyway.

To overclock your processor (assuming your motherboard supports it), go to your BIOS setup page, and use the controls in the Overclock Options category. Make sure you consult the documentation that came with your motherboard or PC for some of the restrictions; for instance, overclocking on your motherboard may be limited by the speed of the installed system memory (RAM).

When you're done, load up Windows and update your Windows Experience Index. Obviously, the Processor score should go up as you dial up the overclocking.

Now, over-overclocking a CPU—overclocking past the point where it's stable—can cause it to overheat and crash frequently, and at the extreme, damage the chip beyond repair. Thus, the most important aspect of overclocking your system involves cooling, so make sure you beef up your computer's internal cooling system before you start messing around with overclocking. (Obviously, your options will be limited here if you're using a laptop.)

Increase your CPU's speed in stages, if possible; don't start off with the fastest setting, or you may end up with a fried processor and lightly singed eyebrows.

If you feel that your system isn't adequately cooled, don't be afraid to add more fans, but beware: do it wrong, and you could actually make things worse. For instance, you need to consider airflow when installing and orienting fans; if the power supply, for instance, exhausts air through the vent in the back of your PC, it must pull it in through the vent near your processor's heatsink. So, make sure you orient the CPU fan so the airflow is as smooth as possible.

Most fans in modern PCs connect directly to special plugs on your motherboard, and are activated when internal thermometers (thermocouples) detect too high a temperature; these typically do a good job of moderating their cooling duties so that they don't produce too much noise. But you may have to tinker with your BIOS settings to make your PC cooler (which can, by itself, improve performance), even if it means a little more noise from your box.

If you're serious about cooling, there are a number of liquid cooling systems that promise to keep hot systems cool. But they're expensive, they work in large desktop PCs only, and they don't necessarily reduce noise.
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