In theory, any hardware installed and operating on your PC requires power, memory, and processor attention. Getting rid of the devices you don't use can speed things up. Some hardware devices, such as wireless network adapters, may also significantly shorten laptop battery life, even if you're not connected to a network, while exposing your notebook to security threats.
If you seldom use your modem, infrared connection, serial port, or parallel port, you can use hardware profiles to disable some or all of these as a group, saving battery power. The implications of this aren't minor: If you need to use your serial port in the future, you'll have to reboot with the hardware profile for that port enabled. But if the need is truly rare, disabling the function is worth the effort. To create a new hardware profile, right-click My Computer (on the desktop or in the Start menu), choose Properties, click the Hardware tab, and then click the Hardware Profiles button. Select an existing profile (you'll probably have just one), and click Copy, then OK. (Copying the existing profile is the easiest way to create a new one.) To make a particular profile the default, use the arrows at the right of the dialog box to move it to the top of the list. Windows will use it the next time it boots. To disable hardware within the current profile, right-click My Computer, choose Properties, click the Hardware tab, and then click the Device Manager button. Right-click the hardware item you want to disable in Device Manager's list (you may need to expand the list first), and choose Disable. (A word of advice: Don't disable any hardware listed under the System Devices category.)
You can also save some of your laptop's battery life (and simplify matters) by ejecting any of the myriad accessories you may have plugged into the laptop, such as PC Cards and flash memory cards; disconnect any USB and FireWire devices, as well. To avoid network complications and strengthen security, use just one network at a time--disable your wireless network connection if you're connected by wire (or if you don't want to use the Wi-Fi card). Most newer laptops with built-in Wi-Fi have a little on/off switch or button on the outside of the laptop's case. Use it.
Here's another important pull-the-plug suggestion: Not every PC needs to be connected to the Internet. If you have a second or third computer, dedicated to children's games or to other duties that don't require a connection, disconnect it from the Internet, literally--just pull out the phone or network cable, or disable the supporting hardware in the Device Manager as described above. If the PC isn't online, it can't catch most viruses.
Running out of free disk space affects performance and obviously prevents you from installing additional programs or creating new documents. You can usually free a significant amount of space by deleting junk files left behind by applications and Web browsers. To jettison the junk, open My Computer, right-click the drive that Windows is installed on, choose Properties, and then click Disk Cleanup. After scanning the drive, Windows will present a list of items, sometimes totaling hundreds of megabytes. Check the items in the list you want to delete, and then click OK.
Frag Your Defragger
And here's one last tip: Don't waste time defragging your hard drive. In the past, by rearranging the sectors of each file on your disk into contiguous and optimized locations, you could boost disk performance. Defragmenting will increase the amount of contiguous free space (which might help you install large programs, like games), but defragging provides minimal performance benefits on most typical PCs (see February's "Defraggers: No Longer Needed?"). Instead, save precious time and try something other than a defrag if you need a speed boost.