Windows Vista supports two very different kinds of file compression. The distinction is confusing but important.
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 has to 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 greatly reduce file sizes. A compressed file often takes up half its original space - even less, in many cases.
Windows Vista's two file compression techniques are as follows:
- Files can be compressed and placed in a "Compressed (zipped) Folder," with an icon to match.
- Files, folders, or even entire drives can be compressed using Vista's file system's (NTFS's) built-in compression capabilities.
Here's where things get complicated.
NT File System (NTFS) compression is built into 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 Vista does all the sleight-of-hand behind the scenes - but the concept can help you remember NTFS compression's limitations and quirks.
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. You might have encountered Zip files on the Internet (they have a filename extension of .zip and they're frequently manipulated with programs such as WinZip, WinZip.com). 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."
If you have Windows show you filename extensions, you immediately see that "Compressed (zipped) Folders" are, in fact, simple Zip files.
Table 1 shows a quick comparison of NTFS compression and Zip compression.
Table 1: NTFS Compression versus "Compressed (Zipped) Folders" Compression
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NTFS |
Zip |
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Think of NTFS compression as a feature of the hard drive itself. |
Zip technology works on any file, regardless of where it is stored. |
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The minute you move an NTFS-compressed 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. |
You can move a "Compressed (zipped) Folder" (actually 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 ether as a compressed file. The person who receives the file can view it directly in Windows Vista, or he can use a product such as WinZip to see it. |
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A lot of overhead is associated with NTFS compression: Windows has to compress and decompress those files on the fly, and that sucks up processing power. |
Very little overhead is associated with Zip files. Many programs (for example, antivirus programs) read Zip files directly. |
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NTFS compression is great if you're running out of room on an NTFS-formatted drive. |
"Compressed (zipped) Folders" (that is to say, Zip files) are in a near-universal form that can be used just about anywhere. |
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You have to be using an administrator account to use NTFS compression. |
You can create, copy, or move Zip files just like any other files, with the same security restrictions. |
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You can use NTFS compression on entire drives, folders, or single files. They cannot be password protected. |
You can Zip files or folders, and they can be password protected. |
If you try to compress the drive that contains your Windows folder, you won't be able to compress the files that are currently in use by Windows.
