The NTFS file system volumes support file compression on an individual file basis. The file compression algorithm used by the NTFS file system is Lempel-Ziv compression. This is a lossless compression algorithm, which means that no data is lost when compressing and decompressing the file, as opposed to lossy compression algorithms such as JPEG, where some data is lost each time data compression and decompression occur.
Data compression reduces the size of a file by minimizing redundant data. In a text file, redundant data can be frequently occurring characters, such as the space character, or common vowels, such as the letters e and a; it can also be frequently occurring character strings. Data compression creates a compressed version of a file by minimizing this redundant data.
While NTFS file system compression can save disk space, compressing data can adversely affect performance. NTFS compression has the following performance characteristics. When you copy or move a compressed NTFS file to a different folder, NTFS decompresses the file, copies or moves the file to the new location, and then recompresses the file. This behavior occurs even when the file is copied or moved between folders on the same computer. Compressed files are also expanded before copying over the network, so NTFS compression does not save network bandwidth.
Files or folders saved into an existing compressed folder will automatically be compressed.
NTFS compressed files and folders will have double blue arrows overlay on their icon at the top right corner to indicate that they are compressed.
This tutorial will show you how to compress or uncompress a file or folder with NTFS Compression in Windows 10 and Windows 11.