What Is a ZIP File and Is It Safe?
When computers used floppy disks and dial-up modem connections, getting a large file off your system and into someone else's hands was a challenge. Today, you can plug a USB thumb drive into a port on your Mac or PC and copy onto it a document larger than the capacity of an early computer's entire hard drive. In 1989, when disk space was at a premium, a computer scientist named Phil Katz created a compression utility called PKZip and a corresponding decompression utility called PKUNZip -- and the popularity of his product changed the face of computing.
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Making Files Smaller
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Back in the days of file-sharing bulletin boards, users logged in via dial-up modems at a fraction of the speed of the slowest broadband connection. Making files smaller reduced their download time. Since many bulletin boards and early online services charged by the minute for a connection, time literally was money. Anything that reduced file size without compromising file contents meant spending less time and money downloading shareware applications to increase productivity.
How File Compression Works
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Zipping applies what is known as lossless or archival compression, meaning that no data are lost when the software makes files smaller, but that zipped files have to be unzipped to be used. Imagine being able to dehydrate your food without harming its texture, flavor or freshness when you rehydrate it, and you understand what archival compression does. In simple terms, the zipping utility, whether PKZip, WinZip, or Windows or Mac OS analyzes file contents, looking for patterns of similarity; where it finds them, it compresses the file size by reducing the redundant content. When you unzip the file, the utility replaces the information and the file becomes usable again.
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Compressed-File Safety
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Zipped files themselves present no intrinsic threat to your computer. That doesn't mean their contents can't hurt you. A ZIP file could contain a malware installer, a piece of child pornography or many other things you wouldn't want on your hard drive. In and of itself, however, the ZIP file format cannot harm you. Just be careful what you unzip on your computer. If you don't know the source of an archive and what it contains, discard it.
Saving Space
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File compression remains relevant despite today's high-capacity hard drives. You may have a fast broadband connection, but that doesn't mean you want to waste time on file downloads. Many types of files compress to a fraction of their unzipped sizes, speeding your access to software updates and other materials. Unless they're zipped first, some types of files -- fonts, for example -- can sustain data damage when you download them through the Internet. Regardless of whether you're saving space, saving time or protecting materials in transit, ZIP files can boost your productivity.
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References
- PKWare: Products
- PKWare: Our Founder -- Phil Katz
- Computer Addicts: "The Rise and Fall of a Software Star: Phil Katz Loved Code -- and Liquor"; Matt Murray et al., 2000
- Microcomputer Applications for Public Administration (PADM 5530): Instructions on Using PKZIP and PKUNZIP (DOS)
- "The Structure of a PKZip File"; Florian Buchholz
- PKZIP Command Line Reference
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