Rar

RAR, short for Roshal Archive, is a proprietary archive file format and data compression technology developed by Russian engineer Eugene Roshal. The .rar file extension is its hallmark, most closely associated with WinRAR, a popular archiver on Windows. The RAR format is not openly standardized; the official specification is proprietary, though independent tools exist to read and, in some cases, write RAR archives.

RAR archives support lossless data compression and a range of features aimed at reliability and efficiency. These include multi-volume archives that span several files, solid archives which use a single shared dictionary for related data to improve compression, and recovery records to help reconstruct data if parts of the archive become damaged. Many versions offer password-based encryption using the AES algorithm, and newer iterations provide options to encrypt file names for additional privacy.

The format has evolved through multiple versions, with newer implementations often referred to as RAR5. RAR5 introduces improvements in compression, larger dictionary and archive sizes, and enhanced data integrity mechanisms, while maintaining compatibility with earlier RAR features.

Usage and ecosystem: RAR remains widely used for distributing large datasets and software due to its strong compression and feature set. It enjoys broad support on Windows and is available on other platforms through cross-platform tools. Open-source extraction libraries, such as UnRAR, enable reading RAR archives in many environments, though writing capabilities can be restricted by licensing terms. In the spectrum of archival formats, RAR competes with open formats like ZIP and 7z, each offering different balances of openness, compression performance, and platform support.