How To Understand Compressed Files

Understand Compressed Files

by Michael E. Callahan aka Dr. File Finder

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Introduction

In the early days of the personal computer, space was a critical issue. Disk space was very expensive so files had to be keep as small as possible. Programmers wrote programs in assembly language to keep them small and efficient. Ahh, but when that wasn't enough, programmers started looking at ways to shrink file sizes.

The personal computer, or PC, was introduced in 1982. Shortly after that a number of shareware compression programs began to appear. These ranged from files with extensions like LBR, for library, to ARC, for archive. Around 1984 ARC became the de facto standard for compressing files. Yet, what exactly are compressed files? Let's take a look.

Packing The Suitcase

One analogy I came up with for compressed files is the suitcase. Think about it. You have socks, shirts, jeans, shorts, toiletries, hair brush, and a book. You have to take all these things with you, but if you carry them they take up too much room. The solution is a simple suitcase. You can pack everything into the suitcase and it all takes up less room. A compressed file is just like a suitcase.

You can take a collection of files and pack them in a compressed file. In order to get at the contents you have to unpack the compressed file. This is a simple, but accurate way of thinking of file compression. You're packing files into a suitcase and making them smaller in the process.

Smaller Files In A ZIP

In 1986 Phil Katz created the ZIP file compression format. It compressed files smaller and much faster than any other program. Within a very short time PKZIP replaced ARC as the de facto compression standard and soon everyone was using "ZIP". Soon even commercial software was including support for ZIP files. Phil Katz made the decision to put ZIP in the public domain and that led to a vast array of programs that could work with ZIP files.

WinZip was the first Windows program for working with ZIP files. In the early days of Windows you could still work with PKZIP from DOS, but many users wanted to stay in Windows so WinZip was a perfect solution.

The screen shot shows WinZip 11 with a ZIP file opened in it. If you look at the files and the file sizes you'll note that some files are compressed more than others. Some graphics file formats, for example, are compressed already so they can't be compressed further. Things like documents and text files generally compress the most and you might be amazed at how much a document can shrink. WinZip has won many awards and is probably the most popular program for working with compressed files under Windows.

Other Compression Formats

Over the years a number of individuals and companies have created alternative compression formats. One of the most popular of these is WinRAR which creates files with an extension of RAR. WinRAR has also won numerous awards and achieves impressive levels of compression.

Other compression formats are used on Macintosh computers and under Linux. Such formats include TAR, GZ, 7ZIP, and many more.

Summing It Up

Compressing files is a great way to decrease file size and increase disk space. It also makes files smaller for sending by email. Compressed files can be password protected and encrypted so the contents are secure. Remember, a compressed file is really just a suitcase that you can put files in. Try out some of the file compression prograss listed below.

• WinZip
• WinRAR
• PowerZip
• ShellZip

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