File and Folder Compression

Windows 2000 supports compression on individual files and on folders for NTFS volumes. Files compressed on an NTFS volume can be read and written by any Windows-based application without first being decompressed by another program. Decompression occurs automatically when the file is read. The file is compressed again when it is closed or saved. Compressed files and folders have an attribute of C when viewed in My Computer.

Only NTFS can read the compressed form of the data. When an application such as Microsoft Word or an operating system command such as Copy requests access to the file, NTFS decompresses the file before making it available. For example, if you copy a compressed file from another Windows 2000–based computer to a compressed folder on your hard disk, the file is decompressed, copied, and recompressed.

This compression algorithm is similar to that used by MS-DOS 6.0 DoubleSpace® and MS-DOS 6.22 DriveSpace®, with one important difference — the MS-DOS functionality compresses the entire primary partition or logical drive, while NTFS enables the user to compress individual files and folders within the NTFS volume.

The compression algorithms in NTFS are designed to support cluster sizes of up to 4 KB. When the cluster size is greater than 4 KB on an NTFS volume, none of the NTFS compression functions are available.

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