Windows PCs slow down over time--that's the popular wisdom, at least.

Your PC's hardware isn't actually becoming slower, though. Startup programs, junk files, and even clumps of dust are just weighing it down. If you give your PC's software and hardware a quick tune-up, it should run like it did the day you bought it. Inexpensive hardware upgrades can even make your PC run faster than it ever did.

Software Tune-Ups

1. Disable or remove unwanted startup programs

Many programs install system tray utilities or services that piggyback onto your system's startup routine, slowing your PC's boot time and wasting valuable RAM. 

In Windows 8, right-click your taskbar, select Task Manager, click More details, and use the Startup tab to disable programs you don't need. The Task Manager even tells you how much time each program adds to your boot process.

In Windows 7, you can use the Startup manager in CCleaner to change which programs start after a boot. In CCleaner, navigate to Tools > Startup. Of course if you don't use a program, you should probably uninstall it entirely from your Control Panel instead of just disabling it.

2. Clean up unnecessary system files

Use a tool like CCleaner or the Disk Cleanup program included in Windows to clear unnecessary files from your PC. These files take up space and can even slow down your PC.

To open the Disk Cleanup program on Windows, start by tapping the Windows key to open your Start menu or Start screen. Type Disk Cleanup, and click the Free up disk space by deleting unnecessary files shortcut in Windows 8 or the Disk Cleanup shortcut in Windows 7.

Use CCleaner if you want to clean up even more types of temporary files. You may want to tweak CCleaner's settings first though, as it will erase your browser history, cookies, cache, and other data you may want to keep.

3. Defragment and optimize your hard drives

Modern versions of Windows defragment drives automatically in the background, so you probably don't have to defragment your hard drive manually. Still, it doesn't hurt to check.

Tap the Windows key to open the Start menu or Start screen, type Defragment, and launch the Disk Defragmenter in Windows 7 or the 'Defragment and optimize your drives tool' in Windows 8. Analyze your drives, and the tool will tell you whether you need to defragment them.

Windows 7's Disk Defragmenter should refuse to defragment solid-state drives, while Windows 8's Disk Defragmenter is now named "Optimize Drives" because it can also optimize solid-state drives.

4. Keep your system free of viruses and malware

Even if you're using antivirus software and otherwise playing it safe, newer kinds of malware can sneak into your system and hog resources. 

The nuclear option is reinstalling Windows entirely and starting afresh. In Windows 8, you can use the Refresh your PC feature to effectively reinstall Windows.  You'll keep your personal files, but you'll get a fresh desktop system and will have to reinstall your desktop software.

On Windows 7, you can use your manufacturer's recovery partition or reinstall Windows 7 from an installation disc.

If you refresh your PC or reinstall Windows from your manufacturer's recovery partition, you'll need to clean up all that nasty bloatware to make it run as fast as possible.

5. Upgrade to a newer operating system

You can also upgrade your PC's operating system. If you have a really ancient PC--maybe you have an old Windows XP PC lying around--you can try installing a lightweight Linux system on it to give it a new lease on life.

Old computers that came with Windows Vista can probably be sped up by updating them to Windows 8.1 or even Windows 7, but it may not be worth the $100 for a new Windows license. You're usually better served putting that money towards newer, faster PC hardware.

Hardware Cleaning

Heat can also cause your PC to slow down over time. If your PC can't cool itself efficiently, it may throttle down your CPU or graphics hardware to operate safely, giving you reduced performance. Excessive heat can damage your PC's hardware over time or cause it to unexpectedly shut down to prevent itself from suffering severe damage.

If you hear your PC's internal fans whirring to maximum speed during light or moderate usage, it may be a sign that your system is overheating.

1. Bust the dust

Give your PC's case a regular cleaning to prevent dust build-up.

While your computer is powered off and unplugged, open up its case and give it a spray with canned air to clean out that nasty dust clinging to fans and blocking vents. Depending on how long it's been since you last cleaned your PC, you may find it surprisingly dusty!

You may also want to try cleaning out your laptop's cooling fans, but opening up a laptop may be more difficult.

2. Replace the paste

Your computer's CPU and GPU use a thermal compound to help dissipate heat. This compound sits between your both your CPU and your GPU and their respective heatsinks. The paste conducts heat from the heat-generating chip to the heatsink. The heatsink is then cooled by moving air pushed by a fan. 

This is similar to how your car cools itself. If you imagine your your CPU or GPU as an engine and the heat sink as the radiator, the thermal paste would be the coolant.

The compound, like the coolant in your car, can deteriorate over time.  This can cause problems cooling your CPU or GPU.

You can disassemble your GPU and replace its thermal paste or remove the heatsink from your CPU and replace the CPU's thermal paste. You'll want a thin, flat, uniform layer of paste.

Hardware Upgrades

Hardware upgrades can also give your PC a new lease on life. Of course, hardware upgrades aren't always the right solution. If your PC is a decade old, you won't be able to speed it up much with a hardware upgrade. You'd be better off buying a new PC entirely. With that in mind, here are the best bang-for-the-buck upgrades.

1. Replace your drives

The bottleneck in most PCs--that is, the slowest part of the PC that you find yourself waiting for most often--is the hard disk.

Solid-state drives are much faster than traditional magnetic hard drives, although they do offer less storage space per dollar. You can get a 120 GB SSD for $100, while you can get a 2 TB--that's over 17 times more storage--magnetic hard drive for about the same price.

If your PC is only a few years old but it seems like the hard disk is the slowest part, you can probably boost its speed by upgrading it with a solid-state drive. You may even be able to upgrade your laptop with an SSD. Whatever you do, be sure to move your operating system and program files to the SSD.

2. Upgrade your Random Access Memory (RAM)

More RAM can help too, but only if your PC doesn't have enough of it already.

RAM holds your PC's working memory. If you have too little RAM, your PC will have to constantly read and write to the pagefile on its hard drive, slowing everything down. If you go this route, be sure you buy the correct type of RAM for your PC.

To install the RAM, power off the PC, open it up, and snap in the new sticks of RAM. Some laptops even allow easy access to their RAM slots so you can upgrade their RAM.

3. Upgrade your CPU or graphics card

Other upgrades are a bit more niche. If you're a gamer and want to run games on higher graphical settings, you may want to upgrade your PC's graphics card.

Bear in mind that your performance bottleneck may be your CPU: If your CPU isn't fast enough, upgrading your graphics card may not help much.

CPU upgrades are possible, but Intel regularly introduces new socket formats, which means new CPUs may not fit in older motherboards. Also note that an Intel CPU won't work in a motherboard with an AMD CPU socket, and vice versa. You may have to upgrade your motherboard as well, and at that point, you may just want to think about buying or building a new computer.

Your old PC hardware won't last forever. New software will eventually become more and more demanding, and your old hardware will one day succumb to entropy and physically break down. Fortunately, some basic system maintenance can extend any PC's usable life. Take care of your PC and it will keep you happy longer.