Zip Files

– Grogan –

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What are Zip Files?

Zip files (.zip file extension) are compressed files, also known as archives and they can contain one or more files and generally are reduced in size due to various compression algorithms employed. One of the main uses of zip files is to make the exchange of files easier. Instead of having to send or download multiple files that might total several Megabytes in size, you send or download only one Zip file, which is considerably smaller because of the use of compression technology.

Common methods of compression include eliminating empty spaces in the file, and eliminating repetitive characters or strings and replacing them with a key (that is much smaller…it is used to regenerate them when the file is de-compressed). Some files cannot be compressed, as they are already in compressed format. Files such as these are merely stored within the archive and no compression is used. An example of this would be an .MP3 sound file, or even including another .zip file within a ZIP archive. Note that there is still some benefit to doing this; simply having the desired files contained in a single archive file is convenient for Internet file transfers and also space is still saved by having everything in one file, as there will be less disk cluster overhang (wasted space due to only partial usage of disk allocation units).

Another advantage of archiving files in .zip file format is that there will be less chance of corruption. If a .zip file gets corrupted, chances are it simply will not open (de-compress or extract). This is particularly significant for download purposes, as if you download a corrupted .zip file and it won’t open you know to just download it again rather than installing a corrupted program or file. The ZIP file format contains a built in Cyclic Redundancy Check algorithm (CRC-32) for error checking both when the file is created, when extracted by utility on the other end, and can be done manually using the program’s test function. Additionally, once created, a .zip file cannot be infected by viruses (provided it was clean when created!!). This means that a .zip file can sit there on a server or in a directory on your hard drive and the programs within cannot be infected.

What does this have to do with me?

First and foremost, many of the files you will be downloading from the Internet will be in .zip format. If you haven’t yet encountered these, you surely will and you need to be able to extract them. Also, you may want to learn how to create your own .zip files to facilitate sending email attachments to others, or simply to save disk space storing files for later use. Now, you need to download a ZIP utility. The next part of the tutorial covers the best utilities available.


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