Windows 7 : Using Compression and Encryption (part 1) - Compressing Drives

When you format volumes with NTFS, you can use compression to reduce the disk space used or encryption to add an extra layer of protection to your data. Because these two options are mutually exclusive, a file or folder can be either compressed or encrypted, not both. Although you can compress or encrypt entire drives, you can also compress or encrypt individual files and folders. Windows 7 Home Premium and Starter do not support NTFS encryption.

NOTE

In Windows Explorer, compressed or encrypted NTFS files and folders are shown in color by default. Compressed files and folders are shown in blue. Encrypted files and folders are shown in green.

1. Compressing Drives

When you format a volume with NTFS, Windows 7 allows you to turn on compression for the entire disk. With compression enabled, any files created on or moved to the disk are compressed automatically. When you open files or access folders, Windows 7 expands the files or folders for viewing as well. This behind-the-scenes compression and expansion makes NTFS compression completely transparent, but it does use some of your computer’s processing power. With that said, there’s an enormous benefit: you can store much more information on a compressed drive.

NOTE

You cannot compress encrypted data. If you try to do so, Windows 7 automatically decrypts the data and then compresses it. Likewise, if you try to encrypt compressed data, Windows 7 expands the data and then encrypts it.

1.1. Compressing a drive

You can compress a drive and all its data by completing these steps:

1. In Windows Explorer or Disk Management, right-click the drive that you want to compress and then select Properties.

2. On the General tab, select “Compress drive to save disk space” and then click OK.

3. In the Confirm Attribute Changes dialog box, shown in Figure 1, specify whether you want to compress only the top-level folder of the drive or the entire drive:

   • To compress only the drive’s top-level folder, select “Apply changes to drive X:\ only.”

   • To compress the drive’s top-level folder, subfolders, and files, select “Apply changes to drive X:\, subfolders and files.”

4. Click OK.

Any files or folders you create on a compressed drive are compressed automatically.

Figure 1. Confirming the compression options

1.2. Expanding a drive to remove compression

If you later decide that you no longer want to compress a drive, you can remove compression from the drive. However, before you do this, you should ensure that the drive has adequate free space to accommodate the expanded files. Typically, you’ll need at least 50 percent more free space on the disk to expand its contents successfully. If a compressed disk currently uses 40 GB of space, this means you’d probably need about 20 GB of free space to expand the disk successfully.

You can expand a disk by completing these steps:

1. In Windows Explorer or Disk Management, right-click the drive that contains the disk that you want to expand and then select Properties.

2. On the General tab, clear the “Compress drive to save disk space” checkbox and then click OK twice.

3. In the Confirm Attribute Changes dialog box, shown in Figure 2, specify whether you want to expand only the top-level folder of the drive or the entire drive:

   • To expand only the drive’s top-level folder, select “Apply changes to drive X:\ only.”

   • To expand the drive’s top-level folder, subfolders, and files, select “Apply changes to drive X:\, subfolders and files.”

4. Click OK.

Figure 2. Confirming the uncompress options