dark mode light mode Search Menu

Zip Files

dougwoods on Flickr

If you’ve ever wanted top send a huge file over the internet, you’ve probably had to “zip it up”. When you zip up a file, it makes the file size smaller so it’s easier to upload and download on the internet. But why do we “zip” files? Where did the terminology come from?

It’s easy to assume that you’re zipping up a file to make it more compact, like you’re bundling it all into one bag. The icon for a ZIP file even has a little zip on it, as if you can pull the zipper down to get at all of your files.

The origin of the ZIP file’s name, however, doesn’t have anything to do with zippers. It actually uses the alternate meaning of “zip” which means “to go fast” — like in the sentence “the cat zipped by when he heard the tuna can open.”

The reason it has this name is because the inventor of the ZIP file, Phil Katz. wanted to make a point. Back when he designed ZIP files, they weren’t called “ZIP files” at all. It went by the much-less memorable name “PKARC.”

However, another company called Systems Enhancement Associates (SEA) didn’t like this very much. This is because they, too, had a system called “ARC” which did a similar job to PKARC. As such, they told Phil Katz that he wasn’t allowed to use PKARC anymore, because ARC was owned by SEA.

Phil Katz was a little disgruntled, but he didn’t let this stop him. Instead, he and a friend decided to create a new format, called “ZIP.” The idea behind the name was that it implied that zipping a file was quick, and — more importantly — faster than using ARC. It was basically telling everyone that their version of the software could beat everyone else’s for speed — a bold claim!

You can imagine how this story went, given how we still “zip” files today, but we never “arc” them. Goes to show that Phil’s ZIP files were, indeed, faster than the competition!

Of course, these days, we tend to think of ZIP files as having zippers on them, because that’s what the icon shows us. It’s a little weird to think, however, that you can “zip up” a digital file to make it take up less room, just like you’re forcing stuff into a bag and trying to get the zipper around before it all falls out again. How do you do that with a digital file?

ZIP files achieve this by finding repeating patterns and structures and simplifying them to cut down on the amount of data a file takes up. For example, take the following sentence:

“I love cats, and I love when cats purr”

In this sentence, the words “I,” “love,” and “cats” appear two times. As such, we can create a “word directory” to make this sentence a lot shorter.

For example, we can assign each word in a sentence to a number. It’d look like this:

1 = I
2 = love
3 = cats
4 = and
5 = when
6 = purr

Not only have we broken down a 9-word sentence into 6 words, but now we can use numbers to re-write the sentence. A single number takes up less space than a word, so we can save bytes by typing our sentence like this:


Now, instead of having to store 38 characters in the original sentence, it only needs to store 11 in our new number-based sentence. That saves a bit of room!

Of course, if you wanted to show this sentence to someone else, you can’t just give them the numbers. After all, they have no idea what each number means!

As such, you’d need to re-translate the sentence by matching each number to each word and writing it back out in English. This is what your PC does when it “unzips” a file; it makes all the files easier for your computer to read.

What ways could you squash down repetitive data to make it take up less space? Who knows — your method may become the next ZIP file!

Learn More

How File Compression Works


Phillip Katz


How to open a zip file


Working with Zip files


History of Data compression


Principles of data compression


Guide to Data Compression


ARC format


Data Compression for kids


Data compression – NASA