If you think about it, there are literally tens of thousands of files on your computer. And each time you install a new application, even more files get added. On top of that, there are all the documents, graphics, and Web pages not to mention graphics the you have collected or created. No matter how you look at it, there's a lot of clutter on your computer.

Worse still, often programs thought you'd gotten rid of often leave bits of themselves behind. These are in the form of "dead" files that aren't used by any other application but which still take up hard drive space.

You can do without a number of the files littering your hard drive. The problem is knowing which files you can safely delete.

Why Not Just Delete Them?

Opening Windows Explorer, highlighting an offending file, and pressing Delete is very tempting. And it can be very dangerous. The file you zap might be one that Windows or one of your applications needs. Without it, the program or even Windows itself may not start properly or at all. Or, you might send the only copy of a document you need for work or some other important reason into digital oblivion. Having to recreate it from scratch can be difficult or, more likely, impossible.

Indiscriminately deleting files can cause problems with the Windows Registry. The Registry is a database that stores software configuration information. When many programs are installed, they add information to the registry. The more software you install, the larger the registry gets. Windows constantly reads the Registry, and having useless entries just slows everything down.

But with a little knowledge, and some care, you can safely delete the files that you don't need.

System Files

Windows needs several different kinds of system files in order to play nicely with the software that you're running. If one or more files goes missing, the finely-balanced harmony goes out the window. On top of that, the Windows itself may not work properly. Or it might stop working all together.

DLL Files

The most important system files are called DLLs. DLL stands for Dynamic Linking Library. They give programs extra functions. When a program starts, Windows loads whatever DLLs the program needs into memory. Over the years, Windows itself and many Windows applications have become dependent on DLLs. So, don't delete any DLL file, no matter how tempted you become. Doing this can damage Windows, one or more programs, or both.

This isn't a hard and fast rule, though. You can search for DLLs and if you find a duplicate, it's safe to get rid of the older file(s). Or, you can delete the files that aren't in a folder under c:windows. Before you delete a duplicated DLL, back it up. If an error message stating that an particular application can't find the DLL appears when you start it, just put the DLL back into the folder.

Driver Files

You also don't want to touch a driver files. These files have extensions like .drv and .vxd, and enable Windows and Windows software to talk to devices like printers, scanners, keyboards, and modems. Because drivers translate instructions between your software and hardware, deleting a driver file will cripple your PC's ability to communicate with the associated device.

Executables

Executables -- the files that actually start an application -- have the extension .exe. So, don't delete any .exe files. You can't start your applications without them. It's especially important not to delete any of the executables in the c:windows folder. When Windows starts up, it loads several programs into memory. Without many of them, Windows will not function properly.

Another set of executables you should never delete are those used to uninstall programs. You'll generally find them in the Windows folder, and they have names like uninst.exe, remove.exe, or unwise.exe. Some have cryptic names like unvise2qt.exe or st6unst.exe. These files are used by the Windows Add/Remove Programs function to uninstall programs. Without these executables, you won't be able to remove a particular program when the time comes.

Documents

Files that you have created -- like word processor documents, spreadsheets, text files, Web pages, or graphics -- are safe to delete. The extensions of documents are too numerous to list. Some of the more popular file formats have extensions like .txt (text files), .doc (Microsoft Word documents), .xls (Excel spreadsheets), and .htm or .html (Web pages).

If you share your computer with others in your home, remember this: if you didn't create it, don't touch it. You don't know whose term paper or budget spreadsheet you're zapping. To avoid accidental deletions, you should always back your documents up by burning them on to a CD, or by uploading them to an online storage site like Yahoo! Briefcase.

Help Files

Windows comes with literally hundreds of help files. And just about every application you put on your hard drive has one. These help files can be useful in explaining the basics of working with Windows or a particular program. Most likely, though, you will wind up using few if any of them. Help files is aren't essential for the running software. So, you can freely get rid of them. But the drawback of deleting a help file is that you'll probably wind up needing it after it's gone. A better option might be to compress the help files into an archive using a program like WinZip.

In Windows, help files have the extension .hlp or .chm. You can find Windows-specific help files in the c:windowshelp folder. For other applications, help files may be in the main program folder, or in a subfolder named Help. Some software developers create online help with HTML files. These load into your default Web browser when you request help in an application. Again, it's safe to delete these files but it might be prudent to archive them instead.

Temporary Files

As they work with data, many applications create temporary files in order to conserve memory and, more importantly, to leave more memory free for processing. Temporary files generally have the extension .tmp, or have file names that start with a tilde (~). For example, myDocument.tmp or ~document.wrd. Programs write temporary files while they are doing something like a spelling check, or as a backup when the program crashes.

Programs usually delete their temporary files when they're shut down. But this doesn't always happen because the program may be faulty, or it may have crashed before you could save a file file. Regardless, programs save temporary files to the folder c:windows emp. Sometimes, especially when you're using a word processor, you'll find temporary files in the folder containing the file you're working on.

Temporary files are safe to delete, especially if the application that created the file is shut down. If it isn't, Windows won't let you to delete the file. You can delete temp files manually by navigating to the c:windows emp folder in Windows Explorer. Once there, you highlight the offending files, and press the Delete button.

A more efficient way to do this is to select Search from the Start menu, then choose Files and Folders. In the window that appears, click the All files and folders option. Then, in the All or part of the file name field, type *.tmp. This will look for all files with the extension .tmp. Click Search. A list of all the temp files Windows find appears on the dialog. Just select the files as you would in Windows Explorer, right click, and then press the Delete button on your keyboard.

A Last Bit of Advice

When deleting files, remember that when in doubt, err on the side of caution and keep the file. Your computer and your data will be safer that way. While deleting files from your computer can be dangerous business, with a little caution you can clean all the junk off your computer without worrying about damaging it. Just remember to keep your eyes open and to think twice before pressing Delete.