You’re using with Windows 2000/XP notebook, and you run across a file you can’t open. What’s more, uou can’t reach anyone for help. You may not be familiar with the type of file you’re dealing with, but you’re pretty sure that the sender or download site indicated that it’s a compressed file.

Here’s some help.

Compressed files, or archives, contain one or more files or folders that have been compacted into a format that takes up less storage space. Much like a trash compactor squashes the air out of garbage to make a much smaller brick out of a pile of rubbish, a file compression utility uses various tricks to reduce a file’s size. One of the most basic such tricks is to remove redundant data. Instead of storing a piece of data for every yellow pixel in a photo of your new car, for instance, an archive might store one yellow dot and a digital note to repeat that pixel as needed throughout the image. Archives are sometimes called zipped files after the ZIP format popularized by the PKZip and WinZip utilities.

Compressing a file or folder means saving it in a new format. There are lots of compressed file formats, but some of the most common have the file extensions .ZIP, .SIT, and .RAR. If you use WinRAR to compress a document named Presentation .ppt, for example, you’ll get an archive called Presentation.rar. Presentation.rar should take up significantly less space on your hard drive than it did in its PPT form, but anyone who wants to open the compacted file will need WinRAR, UnRAR, or some other utility that can decompress the format. After unpacking a file, its extension will revert back to what it was before it was zipped, such as TXT for a text document or XLS for an Excel sheet.

Some compressed files can unpack themselves when you double-click them. Most self-extracting archives have .EXE extensions, though they may be referred to as SFX or other types of files. These can be handy when you want to send someone a compressed file, but you don’t want her to spend time trying to find a suitable decompression utility.

How to decompressed?
Before you do anything else, check to see whether the file is available in another form. If someone emailed it to you, ask him to send you an uncompressed version or an archive in a format your PC can open. This can save you a great deal of time.

No dice? OK, see what Windows can do for you. Win2000 can’t natively open ZIPs or most other compressed files. On the other hand, WinXP will open a wizard to help you decompress most ZIPs when you double-click them. However, WinXP can’t handle them all.

If WinXP can’t open a particular file, compressed or not, it will ask you whether you want it to go online to try to find a utility that can. Select Use The Web Service To Find The Appropriate Program and click OK. When we tried this with a SIT compressed file, Microsoft provided us with a hyperlink to a download page with the StuffIt Expander utility.

Try downloading the indicated program and using it to open the file.

If you don’t want WinXP to go online, choose Select The Program From The List and click OK. Click the checkbox next to the application on your PC that you think might be able to unpack the archive, if any, or click Browse to find one that isn’t listed. Don’t check the box next to Always Use The Selected Program To Open This Kind Of File at this stage. That option says that you’re absolutely sure that you’ve guessed right that the app can unpack the archive, stacked against which is the fact that the program hasn’t already associated itself with opening that type of file. Click OK when you’re done.

StuffIt Expander seems to cover most of the format bases, so it’s a good place to start for your decompression needs. It’s a free utility, but it comes wrapped in a trial version of StuffIt Standard or Deluxe. The StuffIt Standard 15 Day Free Trial option, which didn’t require a credit card as did the Deluxe download.

After Stuff-It 9.0.0.21 is installed, we could open several ZIP and SIT archive files by right-clicking them, choosing StuffIt Archive and Expand Here, and clicking Continue when a nag window popped up.