Zip Files


What are Zip Files?

A zip file format is a file that has been compressed. A zipped file can contain one or many individual files. In either case, each file is compressed individually into one compressed zip file.

Why Zip Files?

It's all about the need for speed. Maybe an example can better explain it:

I have a 4"x6" digital picture that is in the TIFF format and has a storage size of 12,477KB or 12,477,000 MB.

I want to file transfer this image file to another computer on the Internet. For easy calculation, we are going to assume that my connection to the Internet is via a 1 Mb/second connection which equals 1,000,000 bits/second.

From our numbering notes, we know that 8 bits = 1 Byte. This means that our image size is 12,477,000 Bytes * 8 bits/byte = 99,816,000 bits.

If our transfer rate is 1 Mb/second, it should take: 99,816,000/1,000,000 = 99.8 seconds to transfer. 99.8 seconds is equivalent to 1 1/2 minutes which isn't all that long, especially since most broadband connections today will transfer at much higher rates than this. But consider someone who is still using a dial-up line with a connection speed of 40,000 bits/second which was fairly standard 10 years ago. At this rate, it would take 2495 seconds or 42 minutes to transfer.

Well back in the 1980s, a very smart person, Phil Katz, realized that much of the information in a file, especially an image or photographic image, consisted of same color pixels that were next to each other in the image as can be seen in the image below:

zipimage

Even though this image has 74,825 pixels in it, there are less than 20 different colors in it. So, instead of saving this file in the native image format which saved one bit or pixel after another, he devised a way of encoding it so it would give the pixel color followed by the number of same color pixels. What once took 10 bits of space to save, now might only take 4-6 bits. His compression program was originally called PKARC, but as it evolved, was better known as PKZIP and is the grandfather (or mother) of all PC compression programs today.

Now, back to our little example. If we are talking about a file that had an initial size of 20 KB, compressing it is no big deal. But if we get back to our original image that consisted of over 99 Mbs, it can be a big deal. If we compress that image with WinZip in Windows, it will compress to a size of 4.79 MB or 38.32 Mb. If we again use our standard transfer rate of 1 Mb/second, it will now take this file 38 seconds to transfer. This is better than a 60% improvement to our transfer time or reduction in total time by 1 minute. I don't know about you, but if you are waiting for a file to download from the Internet, a minute is a longggggg time.

If you have an interest in learning more about compression and how it works, I would suggest clicking on the following link. It offers some very good explanations that are fairly easy to follow.

How Compression Works

Creating a Zip File

Windows Users -- Using Compressed Folder or WinZip that Comes with Windows

There are many programs available on the Internet for zipping files. If you have MS Windows, which most of you do, it has WinZip built into it and works well if you are exchanging files between Windows based PCs. This would include the assignment zip files that need to be transferred to the PCC student web server. To create a zipped compressed folder and then add files to it, do the following:

Creating the Zipped Compressed Folder

  1. Open My Computer
  • Click the Start button
  • Select My Computer

    WinZip1

  1. Double-click on a hard drive address, then double-click on folders until you have the folder in which you want to create your zipped compressed folder.
  2. When you have opened the folder that you want to create your zipped folder in, click File on the Menu Bar, select New, then select WinZip from the pull down list (this could also say Compressed Folder).

    WinZip2

  3. Type in a name for your new zipped folder. Be sure that it has an extension of "zip". NOTE: Do not confuse a Windows folder with a zipped compressed folder. It is a zipped compressed folder to the zipping utility but it is a file to the Windows system.

    WinZip3

Adding Files to the Zipped Compressed Folder

  1. Select and Drag folders and/or files to this new Zipped Folder

    OR
  2. Locate locate a folder and/or file that you want to add to the Zipped Folder.
  3. Right-click on the folder and/or file, select WinZip or Compressed Folder, then select Add to

    WinZip4

  4. That's all there is to adding files to the zipped folder. As soon as they are added, they will be compressed. You do not need to save the compressed folder/zip file as WinZip has already saved it for you.
  5. Your zip folder (file) is ready to be transferred to a web server or posted to an assignment dropbox.
  6. Other files can be added to it at anytime.
  7. For further information, click the Start Button and select Help and Support. In the Search field, type in WinZip and press the arrow button. From the Suggested Topics list, select "Create a zipped compressed folder"

Windows Users -- Creating a ZIP file with EasyZip

If your Windows does not have WinZip or for whatever reason, you cannot get it to work or don't want to use it, you can download a zipping program from the Web. One that is available for free and which seems to be fairly easy to use is called EasyZip. If you choose to download and use this program, after you download EasyZip to your PC and install it, you can create a ZIP file by doing the following (NOTE: Just about every Zip program has this same format so these instructions could be used for others as well):

  1. Click on the EasyZip program to start it. You should see the following window:

    EasyZip1
  2. Click on the New button to create a New zip archive.

    EasyZip2
  3. In the Look in field, select the folder in which you want to save your ZIP file.
  4. In the File name file, type in a name for your zip file.
  5. Click the Open button.

    EasyZip3
  6. The Add window will appear. Select the files that you want to ADD to the zip file.
  7. Click the Add button to add the files to the zip file.

    EasyZip4
  8. Click the "X" to close the window, or click the Add button to add more files.
  9. That's all there is to creating a zip file. When you click the Add button in step 7, the files are compressed and added to the zip file. The zip file is then ready to transfer to a web server or to be submitted to an assignment drop box. You do not need to Save the file as EasyZip has already created it for you.

There is also a brief tutorial that comes with the EasyZip program. To access, do the following:

  1. Open EasyZip

    EasyZipTut1
  2. Click Help on the Menu bar and select Brief Tutorial. This will bring up the EasyZip tutorial in your browser window.

    EasyZipTut2
  3. Click on a link to see information on the associated function.

Mac Users

OS X apparently comes with built-in zip capability (who would expect anything less). The link below says it all, so please click on the link if you don't already know how to do this:

Making Zip Files on the Mac

StuffIt is a very popular Mac zipping program but it is commercial and thus not free.

Another stand-alone zipping program that seems to be quite popular for the Mac is one called MacZip. If you think you would like to try it, click the following link to download. I'm sure that little bitty screen shot has useful information on it, but your eyes will have to be better than mine to read it.

MacZip