Compressed archives combine multiple files into a single file to make them easier to transport or save on diskspace. Archiving software may also provide options for encryption, file spanning, checksums, self-extraction, and self-installation. Zip is the most-widely used format, used by the Windows operating system and more recently by OSX as well. RAR is also a very popular and flexible format. Unix uses the tar file format, while Linux uses the tar and gz format.