Mysterious ZIP file does big things in a small way

Your computer

March 01, 1998|By Michael Himowitz

FOR NEWCOMERS to the World Wide Web, the ZIP file is one of the great mysteries of life. Consider the reader who sent this e-mail query: "I tried to download a program with my Web browser and what I got was something called a ZIP file. When I clicked on it with my mouse I got this weird message and nothing happened. What did I do wrong?"

You just haven't taken the final step, which is turning the ZIP file into the program you want. And for that, you'll need some additional software -- which you can also find on the Web. But first it helps to know exactly what a ZIP file is.

A ZIP file is a handy way to store information and squish it so that it takes up less space on your disk drive and less time to transfer, whether you're downloading it from the Web or sending it directly to another computer over a modem.

A ZIP file -- technically, a "compressed archive" -- usually contains more than one file, perhaps dozens or even hundreds. Why would you want to combine so many files into one? Well, archiving makes it quicker and easier to transmit those files from one place to another. You also don't have to worry about losing anything. This is a critical issue when you transfer software, because most programs are actually large collections of files, each of which has to be in the right place for the software to work properly. A ZIP file is also compressed, which means that it's a lot smaller than the sum of the files it contains. Compression is a big deal in the computer world because it costs money to store information and send it over phone lines. The less information you have to store or transmit, the less you spend.

So how do you compress data? As it turns out, most of the information we create is quite repetitive. For example, this column contains frequent repetitions of common sequences of characters, such as the word "the." Digitized photos with large areas of the same color contain millions of identical dots. The file that contains your company's mailing list may allocate 32 characters for each name, even though most names occupy no more than 20 characters.

This waste of space has tantalized mathematicians and programmers since the dawn of computing, and over the years they've developed software for compressing all kinds of information -- sometimes by ratios of as much as 100 to 1. For computer programs and business data, you can expect ratios as high as 10 to 1. The compression you get depends on the type of information in your files and the software used to compress it.

Archives with the ubiquitous .ZIP extension are compressed according to a formula developed by Phil Katz, a talented programmer and gifted marketer who developed compression software called PKZIP in the late 1980s.

It's not the best compression system ever developed, but it works well enough, and over the years it has become a standard in the PC world.

To use a ZIP file that you've downloaded, you'll need a program that can unpack it and extract the original files. But you might as well get one that can create ZIP files, too, because they're very useful.

For example, the 50 Microsoft Word files that contain the columns I wrote for The Sun last year occupy 2.7 megabytes of hard disk space. Naturally, I want to keep my deathless prose handy, but I don't necessarily need to access every one of those columns every day. So I ZIPped them into a single file that occupies less than half a megabyte of space. That sure got rid of the hot air.

The same software that ZIPped them up can extract all the columns or any particular column whenver I want. And if I run out of hard disk space, I can easily store the ZIP file on a single floppy.

There are dozens of ZIP utility programs available on the Web. Luckily, you won't need an unZIPping program to use most of them because they'll install themselves automatically. The better programs will also handle files compressed in different formats used by Unix and Apple Macintosh systems.

The most popular of the bunch is Nico Mak's WinZIP, a $29 shareware program which is available for downloading at www.winzip.com.

You might also consider the latest Windows version of Phil Katz's original at www.pkware.com. If you're adventurous, dozens of other ZIP programs are available on the Web's big shareware centers. Check out Cnet's www.shareware.com or Ziff Davis' utility archive at www.zdnet.com.

I do my own ZIPping with Norton File Manager, which is part of Norton Navigator -- a superb set of Windows 95 utilities that everyone should have. You can download a trial version at www.symantec.com.

To contact Mike Himowitz, send e-mail to: mike.himowitaltsun.com.

Pub Date: 3/01/98

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