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Zipping and Compressing

Windows supports two very different kinds of file compression. The distinction is confusing but important, so bear with me.

File compression reduces the size of a file by cleverly taking out parts of the contents of the file that aren't needed, storing only the minimum amount of information necessary to reconstitute the file - extract it - into its full original form. A certain amount of overhead is involved because the computer must take the time to squeeze extraneous information out of a file before storing it, and then the computer takes more time to restore the file to its original state when someone needs the file. But compression can reduce file sizes enormously. A compressed file often takes up half its original space - even less, in many cases.

How does compression work? That depends on the compression method you use. In one kind of compression, known as Huffman encoding, letters that occur frequently in a file (say, the letter e in a word-processing document) are massaged so that they take up only a little bit of room in the file, whereas letters that occur less frequently (say, x) are allowed to occupy lots of space. Rather than allocate eight 1s and 0s for every letter in a document, for example, some letters may take up only two 1s and 0s, and others can take up 15. The net result, overall, is a big reduction in file size. It's complicated, and the mathematics involved get quite interesting.

Following are the two Windows file compression techniques:

  • Files can be compressed and placed in a compressed (zipped) folder. The icon for a zipped folder, appropriately, has a zipper on it.
  • Folders or even entire drives can be compressed by using the built-in compression capabilities of the Windows file system (NTFS).

Here's where things get complicated.

NT file system (NTFS) compression is built in to the file system: You can use it only on NTFS drives, and the compression doesn't persist when you move (or copy) the file off the drive. Think of NTFS compression as a capability inherent to the hard drive itself. That isn't really the case - Windows does all the sleight-of-hand behind the scenes - but the concept can help you remember the limitations and quirks of NTFS compression.

Although Microsoft would have you believe that compressed (zipped) folder compression is based on folders, it isn't. A compressed (zipped) folder is really a file - not a folder - but it's a special kind of file, called a zip file. If you ever encountered zip files on the Internet (they have a .zip filename extension and are read and created directly in Windows File Explorer). Zip files contain one or more compressed files, and they use the most common kind of compression found on the Internet. Think of compressed (zipped) folders as being zip files, and if you have even a nodding acquaintance with zips, you'll immediately understand the limitations and quirks of compressed (zipped) folders. Microsoft calls them folders because that's supposed to be easier for users to understand.
If you have Windows show you filename extension, you see immediately that compressed (zipped) folders are, in fact, simple zip files.
Zipping is very common, particularly because it reduces the amount of data that needs to be transported from here to there. NTFS compression isn't nearly as common. It's more difficult, and hard drives have become so cheap there's rarely any need for most people to use it.

Below shows a quick comparison of NTFS compression and zip compression.

NTFS Compression versus Compressed (Zipped) Folder Compression

  • NTFS
    Think of NTFS compression as a feature of the hard drive itself.
  • Zip
    Zip technology works on any file, regardless of where it is stored.

  • NTFS
    The minute you move an NTFScompressed file off an NTFS drive (by, say, sending a file as an email attachment), the file is uncompressed, automatically, and you can’t do anything about it: You’ll send a big, uncompressed file.
  • Zip
    You can move a compressed (zipped) folder (it’s a zip file, with a .zip filename extension) anywhere, and it stays compressed. If you send a zip file as an email attachment, it goes over the Internet as a compressed file. The person who receives the file can view it directly in Windows or use a product such as WinZip to see it.

  • NTFS
    Lots of overhead is associated with NTFS compression. Windows must compress and decompress those files on the fly, and that sucks up processing power.
  • Zip
    Very little overhead is associated with zip files. Many programs (for example, antivirus programs) read zip files directly.

  • NTFS
    NTFS compression is helpful if you’re running out of room on an NTFS-formatted drive.
  • Zip
    Compressed (zipped) folders (that is to say, zip files) are in a near-universal form that can be used just about anywhere.

  • NTFS
    You must be using an administrator account to use NTFS compression.
  • Zip
    You can create, copy, or move zip files just like any other files, with the same security restrictions.

  • NTFS
    You can use NTFS compression on entire drives, folders, or single files. They cannot be password protected.
  • Zip
    You can zip files, folders, or (rarely) drives, and they can be password protected.
If you try to compress the drive that contains Windows itself (normally your C: drive), you can't compress the files that are in use by Windows.

Compressing with NTFS

To use NTFS compression on an entire drive, follow these steps:

  1. Make sure you're using an administrator account.
  2. Bring up File Explorer by clicking the File Explorer icon. On the left, choose This PC.
  3. On the left, tap and hold down (or right-click) the drive you want to compress. Choose Properties, and click the General tab.
  4. Select the Compress This Drive to Save Disk Space check box. Then click OK.
    Windows asks you to confirm that you want to compress the entire drive. Windows takes some time to compress the drive; in some cases, the estimated time is measured in days.

To use NTFS compression on a folder, follow these steps:

  1. Make sure you're using an administrator account.
  2. Bring up File Explorer by clicking the File Explorer icon. On the left, choose This PC.
  3. On the left, tap and hold down (or right-click) the folder you want to compress. Choose Properties, and click the Advanced button.
  4. Select the Compress Contents to Save Disk Space check box. Then click OK.
    Windows asks you to confirm that you want to compress the folder. Unless the folder is enormous, it should compress in a few minutes.
To uncompress a folder, reopen the Advanced Properties dialog box (right-click the file or folder, choose Properties, and click the Advanced button) and deselect the Compress Contents to Save Disk Space check box.

Zipping the easy way with compressed (zipped) folders

The easiest way to create a zip file, er, a compressed (zipped) folder, is with a simple tap and hold down (or right-click). Here's how:

  1. Navigate to the files you want to zip.
    Usually you find them using File Explorer, although there are other ways. For File Explorer, click the Start icon and then the File Explorer icon. On the left, choose This PC.
  2. Select the file or files that you want to zip together.
    You can tap and hold down, or Ctrl+click to select individual files, or Shift+click to select a bunch.
  3. Tap and hold down (or right-click) any of the selected files, and choose Send To → Compressed (Zipped) Folder.
    Windows responds by creating a new zip file with a .zip filename extension and placing copies of the selected files inside the new zip folder. File Explorer selects the file and shows a Compressed Folder Tools context tab. Double-click the new file (er, folder).
    The new zip file is just like any other file: You can rename it, copy it, move it, delete it, send it as an email attachment, save it on the Internet, or do anything else to it that you can do to a file. That's because it is a file.
  4. To add another file to your compressed (zipped) folder, simply drag it onto the zipped folder icon.
  5. To copy a file from your zip file (uh, folder), double-click the zipped folder icon and treat the file the same way you would treat any regular file.
  6. To copy all files out of your zip file (folder), click the Extract tab on the File Explorer ribbon.
    From there, you can choose the location or click the Extract All icon to choose a location other than the ones offered.
By default, the Extract All icon recommends that you extract all the compressed files into a new folder with the same name as the zip file, which confuses the living bewilickers out of everybody. Unless you give the extracted folder a different name from the original compressed (zipped) folder, you end up with two folders with precisely the same name sitting on your desktop. Do yourself a huge favor and feed the wizard a different folder name while you're extracting the files.