Archive and Compressed FilesAn archive file is a file that contains other files. It's a bundle of files packaged together. Groups of files that belong together are archived because it's easier to move one bundled file from one place to another than it is to transfer many individual files, one at a time.
Most archived files are also compressed (shrunk in size) during the archiving process. A bit about how file compression works.
Life, not already sufficiently complicated to suit software developers, provided the opportunity for the development of different kinds of archivisational methods. Archive types can be distinguished by the file extention. The most common are .ZIP, .ARC, .LZH, and .ARJ for PCs; (.SIT for Macintosh). Each of them (and the other less commonly used archive types) each require a different utility (i.e. small program) to extract the individual files.
One more file extension is worthy of note. Archived files with an .EXE extension (.SEA for Macintosh) are self-extracting files. No separate utility is required.
Compressed files are files that have been temporarily shrunk to make it easier to transfer them from one place to another. Frequently, compressed files are bundled together and archived, as described above, so that groups of files can be transferred as one file.
There are untold numbers of compression methods. They work by searching for and replacing characters with codes. By analyzing actual data content, strings of blanks can be replaced with a code that represents them. Some replace long sequences of repeating characters with one occurance of the character and a number. For example, a sequence of 50 spaces is replaced with one space and the number 50. Some compression programs create a dictionary, a table that stores information. Groups of characters that occur more than once are replaced with codes. For example the word, "Rumplestiltskin," if it occurs more than once, is replaced by a short code. The dictionary provides the means during the decompression process to restore the original words and characters. Back to Archive files
Encoded files serve a different purpose. They enable files to be sent as email file attachments.
PC UTILITIES7-zip (free)
MAC and PC UTILITIESThe Unarchiver (free)
iZip for Mac (free)
Almost all Macintosh computers can now accommodate .ZIP and other PC files.