What Happens When Large Files Are Zipped

Video Transcript

"Hi, my name is Dave Andrews and today I'm going to talk to you a little bit about what happens when a large file is zipped. Now when you take a file and you zip it, basically you're compressing it. And the way that compression works is that it will scan your entire file and it will look for patterns that it can repeat. Basically once it finds a large pattern within a document, instead of having that pattern appear three times, or as many times as it appears, it'll take the pattern, it'll save it once in the document, and then it will keep track of where it appears after that. Just basically by a number such as it appears at space twenty or it appears at space forty-five. That way it doesn't copy that actual pattern three or four or more times, it just has a copy of it once and then where it appears later on. So I'm going to show you an example of this if we'll go to the computer. I have on my desktop a file called myfile.text. I'm going to open it up here. It's basically a very, very large text file that is just copies of the text asdf, asdf, asdf, over and over and over. Now asdf here is going to be the pattern that our compression algorithm finds and since it's repeated over and over and over again, you should get really good compression when we run it through a zip process. Now, to zip that file, I'm going to right click on it, and I'm going to go to send to, and I'm just going to click on compressed folder. Now, what that has done, is that has just created a new file on my desktop called myfile.zip. If I go to the properties of this file, as you can see it is sixteen point three kilobytes. My original file was sixteen megabytes. So that's a difference of - here is sixteen point seven million bytes that are stored on the hard drive, as opposed to sixteen thousand seven hundred and eleven bytes. So there's a huge compression ratio there because that asdf pattern happens so many times in that file. My name is Dave Andrews, and I've just talked to you a little bit about what happens when large files are zipped."