h2. What are archive (.zip) files?
An archive contains one or more files in a compressed format. Archive files created by the most commonly used archiving software have file names that end in .arc, .arj, .rar, or (most often) .zip. Files of any type--programs, text, or graphics--may be packed in such archives.
An archive is generally much smaller than the actual size of the file or files it contains. When archived, a file can be reduced in size by as much as 60 percent, depending on the type of data it contains. The smaller size makes it faster to download.
A few file types, including .gif graphics files, can be stored--but not compressed--in an archive. A given archive may contain from one file to dozens, allowing you to get all the files for a game, spreadsheet, or other program in a single download.
h2. How do I open archive files?
A particular kind of utility is required to put files into an archive; some examples are PKZip, PowerArchiver, WinZip, and WinRAR. The same program, or another that supports the format used, is required to "unpack" archived files.
Both Windows XP and Vista can create or unpack files in the .zip format natively. To extract files, simply select the .zip file, right-click it, and choose the Extract All option. Use the Send to/Compressed Folder option to create such a file. You also can unpack .zip and other types of archives in PC World's Downloads library with any of the archiving utilities mentioned above; you can find them, and a number of others, under the Compression category in the Downloads library.
h2. What are self-extracting archives, and how do I handle them?
Most .exe files that you download are self-extracting archives that do not require use of another program to unpack the files. As its name suggests, a self-extracting archive unpacks its own files when you run it.
It's a good idea to unpack the files in a folder set aside for that purpose, such as My Downloads. A self-extracting archive may contain installation files that will be left on your hard drive after you install the program; you'll want to keep those files in one place so that you can delete them easily later.