How 7-Zip Handles ARJ and LZH Legacy Archives

7-Zip provides built-in, read-only compatibility for vintage archive formats such as ARJ and LZH (also known as LHA). While modern workflows rarely rely on these formats, 7-Zip enables users to open, inspect, and extract contents from them without requiring original DOS or vintage platform utilities. However, 7-Zip intentionally restricts its functionality for these formats strictly to decompression, meaning you cannot create or modify ARJ or LZH files.

Decompression and Extraction Capabilities

7-Zip includes native decoders capable of parsing the file structures and compression algorithms associated with ARJ and LZH containers.

  • LZH/LHA Support: 7-Zip can decompress most standard LHA compression methods, including the common -lh0- (stored), -lh4-, -lh5-, -lh6-, and -lh7- algorithms. This allows users to recover historical data created on platforms like Amiga, PC-98, and early MS-DOS systems.
  • ARJ Support: 7-Zip parses standard ARJ archives created by Robert Jung's original DOS utility, allowing for the extraction of files compressed using standard ARJ compression methods.

Users can interact with these files through both the 7-Zip Graphical User Interface (GUI) and the command-line interface. Using the command 7z x archive.arj or 7z x archive.lzh will extract the contents while preserving directory hierarchies.

Lack of Compression Support

7-Zip operates under an asymmetrical format model: it unpacks dozens of legacy formats, but it only packages files into a select group of modern formats (7z, ZIP, GZIP, BZIP2, TAR, WIM, and XZ). Because ARJ and LZH have been superseded by algorithms offering superior compression ratios, stronger integrity checks, and modern metadata support, 7-Zip does not offer the ability to pack new archives in either format.

Multi-Volume and Encrypted Archives

Handling advanced features of these legacy formats comes with specific limitations:

  • Split Archives: Multi-volume ARJ archives (typically using .arj, .a01, .a02 extensions) can generally be unpacked as long as all constituent parts reside in the same directory and the primary archive header is intact.
  • Encryption: Standard, unencrypted legacy archives open seamlessly. However, ARJ archives utilizing proprietary or obscure legacy encryption routines may fail to decrypt properly, as modern tools prioritize standard cryptographic implementations over deprecated, vendor-specific ciphers.

Integrity and Safety

When processing ARJ and LZH files, 7-Zip applies modern path-sanitization rules. It strips out unsafe relative directory paths (such as ../ traversal attempts) embedded in malicious or corrupted legacy files to prevent unauthorized file overwrites during extraction.