Reader Leo writes: Lately I notice that Windows tells me i have low disk space quite often. When I start my computer I might have 800MB of free space, but after a few hours I get a warning from Windows and my drive shows less than 200MB of free space. Could this be a virus?

Many people don't realize that Windows makes prodigious use of your hard drive, even if you aren't installing new programs or creating new files. Through temporary files and the notorious swap file (the repository of "virtual memory" for when you run out of RAM). Want to see how big it is in the flesh? Just look on the C: drive (in the root folder) for "pagefile.sys." My pagefile.sys is 1.5GB in size. I'll discuss how to change this in a moment. But anyway, no, you don't have a virus. You're a victim of not having a big enough hard drive.

Let's start with how to attack this problem the easy way. First, let's try to clear off some space. You can start by getting rid of any files you don't need (got any old podcasts or video downloads clogging up your hard drive? toss 'em). You should also delete any old emails you no longer need, and make sure you empty them out of your deleted items folder.

Next take a spin with Windows Disk Cleanup (under Start > Programs > Accessories > System Tools). Disk Cleanup will scour your drive for excess junk (like temporary files and old installers you don't need), and give you the option to delete them. You can also consider compressing old data files (Disk Cleanup will do this for you). Disk Cleanup is usually good for a few gigabytes of newly free space if you haven't run it recently. While you're at it, remember to uninstall any programs you don't use any more, using the Add/Remove Programs control panel.

Another useful trick is to throttle down System Restore settings. Go into the Windows System control panel and click the System Restore tab. By default, System Restore is set to use "Max" disk space: 12 percent of your drive. You can safely knock this down to 5 percent with minimal risk. On a 60GB drive, that equals more than 4GB of newly freed space.

Also in the System control panel, you can decrease the size of your swap file, though be warned, this could hurt performance. Click Advanced, then under Performance click Settings. Click Advanced again then look at the bottom of that tab. Your current virtual memory page file size will be noted. Click Change to throttle it down, though you should never go below the amount of your physical RAM. I recommend tweaking this only as a last resort.

After that, you can try shareware apps designed to free up disk space, but I don't really recommend them. A fresh Windows install will likely free up space too, but only if you back up the drive and reformat it. Again, that's probably more trouble than its worth. If these tips don't help you, you're probably just have too much data to fit on your hard drive. Consider adding a second drive (external models connect easily with USB) or, just maybe, upgrading the whole shebang. Good luck.