We’ve all had the experience of downloading some goodie over the Internet, only to discover that it’s packed up in some file archiving and compression format. There are dozens of formats kicking around out there, and it seems like no sooner are you equipped to handle five formats than some joker hands you a sixth. Why do we need so many? Wouldn’t it be nice to have a standard? Yeah, right, dream on…
.zip The closest we have to a standard. The most common archive/compression format is easily accessible both to pack and unpack across every major platform. Opens with PKZIP & WinZIP on Windows, a built-in handler on Mac OS X v10.3+, and with the ‘unzip’ command on Unix-likes.
.7z The next-best to ZIP. The 7-zip program handles a broad variety of formats, including .cab, .rar, .Z, .gz, .bz2, and others. It is ported to the Windows platform as 7z.exe, the Mac OS X platform as 7zX, or the Unix-alike platforms as 7z.
.gz The GNU zip program, native to Unix-likes. Opens on Windows with WinZIP, 7-zip, or Power Archiver, on both the Mac OS X and Unix-likes using ‘gunzip’ command.
.bz2 The Bzip2 program, native to Unix-likes (originally BSD). Opens with 7-zip on Windows, ‘bunzip2’ command on Unix-likes and Mac OS X.
.tar, .tar.gz, .tar.bz2 The Unix-based ‘tar’ program takes a little explanation. Tar stands for ‘tape archive’ and was originally for archiving files backed up to huge reels of tape running on mainframes. So it’s still used today for archiving (making one file out of many) and the gzip/bzip2 programs are for compression (packing one file into a smaller space), which is a different function. As opposed to ZIP and 7-zip, gzip and bzip2 don’t handle archiving in the same step. So the most common archive you’ll see coming from Unix-likes is a .tar.gz or .tar.bz2, and they’re usually called ‘tarballs’. The reason why it is more efficient to archive first and then compress is an exercise for the reader (or the subject of a whole new article). Opens with 7-zip on Windows, and of course the ‘tar’ command on Unix-likes and Mac OS X.
.rar Windows’ revenge on Unix for tar. Opens with 7-zip on Windows, UnRarX on Mac OS X, and unrar on Unix-likes. Proprietary and patented, so available only as freeware at best, not free software.
Below are some extreme edge cases. If anybody hands you one of these files, you are within rights to send it back with a note asking for a more standard format.
.zz The Zzip program, created for Windows/Unix systems and still under development. Not yet ported to Mac OS X, to my knowledge. Allegedly opens with the zzip program somehow. May be great someday, but too young right now to be viable.
.z, .Z These are created with the Unix-only ‘pack’ and ‘compress’ programs, respectively. Ancient programs from the heavy iron days of Unix mainframes, nobody in their right mind has used this format in 20 years. Compress has a Mac OS X port, and 7-zip can handle a .Z file, but really these formats are dead.
This is barely scraping the surface – there are dozens of even wackier programs out there, but most of the archived/compressed files you download from the Internet will be one listed here. A note on etiquette: When packing files to send, do put them all in one folder so the unsuspecting recipient doesn’t get a file-bomb exploding all over their home directory. And do try to use standard programs that are widely portable whenever possible.
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