What is Zip?


Zip is a compressed file archive format. Zip files, called archives, are container files that usually contain a number of files compressed for portability or long term storage. Depending on the compression level specified at the time the zip file was created, and on the type of data stored, zip archives can be as small as one-tenth the size of the original files. Thus, zip is a convenient format for transferring files over the Internet, where bandwidth is critical, and also for long-term storage of documents where disk space is limited. Additionally, zip files provide limited document security by offering simple password protection on archives.

Zip files were developed as a replacement for ARC file archives, the first archives that natively included compression features. Early compression implementations by the creator of zip were heavily based upon the ARC format, and only after a copyright infringement lawsuit was the independent zip format developed. Zip was not only extremely fast, it was also an open standard, thus it became very popular among early BBS downloaders. Within three years of it's introduction, zip support was built into all major file managers on the Windows, Linux, and Macintosh operating systems. Most of these could handle the archives in a transparent manner, including drag and drop capabilities. Thus, working with zip archives was very similar to working with regular file directories.

The Zip file format has several technical limitations and drawbacks. Most importantly, the password protection feature uses a known-broken algorithm. Early versions of zip had 4 GB file size limitations, and although later versions have workarounds in place, they are not widely supported. Zip files also have a timestamp resolution of two seconds, an artifact of the two-second NTFS timestamp resolution. Although zip files themselves are considered to be safe from viral infection, they can contain infected files and hide them from virus scanners. A final drawback of the zip format is the fact that zip compresses each file in an archive individually. While this allows individual files to be read without decompressing the entire archive, it is an inefficient use of the compression algorithms used.

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