Compressing and Uncompressing Folders and Files

Each file and folder on an NTFS volume has a compression state, which is either Compressed or Uncompressed. The compression state of a folder does not reflect the compression state of the files in that folder. For instance, a folder can have a compression state of Compressed, yet all of the files in that folder could be Uncompressed. Or some of the files in an Uncompressed folder could be Compressed.

You can set the compression state of folders, and compress or uncompress files by using My Computer, Windows NT Explorer, or a command-line program called Compact. When using My Computer or Windows NT Explorer, you can set the compression state of an NTFS folder without changing the compression state of existing files in that folder.

You can set My Computer and Windows NT Explorer to display compressed files and folders with a different color than uncompressed files and folders. On the View menu, click Options. On the View tab, check Display compressed files and folders with alternate color.

Note

Compressing the page file does not accomplish much. Windows NT does not compress an open page file, so the user sees an error message box. When trying to compress a closed paging file, the file is compressed without warning (as with any other file). When you restart Windows NT, the page file automatically reverts to the uncompressed state. For information about the page file, look at topics for virtual or virtual memory in Windows NT Help.

Using My Computer or Windows NT Explorer

Each of these programs provide the same compression functionality on NTFS volumes. With My Computer or Windows NT Explorer, you can:

Set the compression state of an NTFS folder to Compressed or Uncompressed.

Specify whether to compress or uncompress all files in the folder when you change the state of the folder to Compressed or Uncompressed.

Compress or uncompress individual files in the folder.

To set the compression state of the folder:

1. Select the folder you want to compress or uncompress.

2. On the File menu, click Properties to display the Properties tab.

Select or clear the Compressed check box.

My Computer or Windows NT Explorer pop up a dialog box asking whether all the files and subfolders in the folder should be compressed or uncompressed. Existing files or subfolders in the NTFS folders retain their compression state unless you select Yes in this dialog box.

To work with individual files:

1. Select the folder you want to compress or uncompress.

2. On the File menu, click Properties to display the Properties tab.

3. Select or clear the Compressed check box.

You can also use the Properties tab to view the compressed size and compression ratio of the selected file.

Using the Compact Program

The Compact program is the command line version of the compression functionality in My Computer or Windows NT Explorer. The Compact command displays and alters the compression of folders and files on NTFS volumes. It also displays the compression state of folders.

There are reasons why you would want to use this program instead of My Computer or Windows NT Explorer:

You can use Compact in a batch script.

If the system crashed when compression or uncompression was occurring, the file or folder is marked as Compressed or Uncompressed, even if the operation did not complete. You can use Compact to force the operation to complete.

Note

Unlike My Computer or Windows NT Explorer, the Compact program does not prompt you on whether you want to compress or uncompress files and subfolders when you set the compression state of a folder. It automatically does the compression or uncompression of any files that are not already in the compression state you just set for the folder.

For more information about this program, type compact /? at the command prompt, or see "File System Utilities" in Chapter 22, "Disk, File System, and Backup Utilities."