Your Windows PC is slowing down. Maybe it takes longer to boot up or shut down. Perhaps the hard drive grinds in the background constantly. Or maybe launching an application takes much longer than it once did.

And although Windows 7 is speedier than previous versions, it can still become sluggish, particularly if you install and uninstall a lot of applications.

Over the next few pages we'll look at what it takes to clean the junk from your system and get rid of the detritus that has built up over time. We'll specifically discuss boot times, hard drive issues and the mysterious Windows Registry. We'll also explain how you can help stave off potential future problems, not least by getting out of habits that are likely to lead you to create unnecessary files in the first place.

Mysterious PC slowdowns: the suspects

Sometimes a PC will start to crawl without warning and the reason isn't always obvious. Although the focus of this article is on cleaning and preventing operating-system gunk, we'll start by touch briefly on a few hardware problems that can cause sudden slowdowns.

Vanishing memory
If you built your system yourself (see Build your dream PC), the Bios may on occasion reset itself without your knowledge. This can happen during a power failure, or if you shut down the system during the POST (power on, self test) process. During such a reset, the memory speeds may revert to something more conservative. You'll notice performance issues only when running memory-intensive programs.

Another possibility is that the apparent amount of memory might shrink. For example, on recent motherboards built with Intel's P55 and X58 chipsets, a heatsink that's too tightly mounted can bend memory circuit traces on the motherboard. The net result is that one memory module becomes invisible to the system, potentially reducing the amount of memory available to Windows by a third or a half. That hampers your system, particularly when applications and data are swapped to virtual memory on your hard drive.

Modern Intel and AMD CPUs will automatically throttle down if they get too hot. This can happen if your system's CPU and case cooling fans become coated with dust and start slowing down. Make sure you check the system temperature in the Bios or using any utilities that may have been provided along with your motherboard.

Imminent hard drive failure
As hard drives begin to develop bad sectors, they try to copy data to safe sectors. Ordinarily this occurs rarely, but when a drive starts to fail, the behaviour could become more frequent. The net result is constant disk use – also described as disk thrashing - as the system attempts to find free, good sectors. If you suspect such activity, turn on the SMART feature in your PC's BIOS, which will pull diagnostic information from the drive and warn you if failure seems imminent.

NEXT PAGE: Windows entropy explained

  1. Undo the damage caused by everyday computing
  2. Windows entropy explained
  3. Diagnostic tools: tracking down the junk
  4. More cleanup options
  5. Useful third party choices
  6. Maintaining a clean system