UPX 5.1.1 – Free Ultimate Packer for eXecutables

UPX (Ultimate Packer for eXecutables) is a free, portable, and high-performance executable packer that supports many popular executable formats. It helps developers and power users reduce file size efficiently while keeping applications easy to distribute and deploy.

This executable packer achieves high compression ratios while maintaining fast decompression performance. Thanks to in-place decompression in most formats, packed executables run efficiently with no extra memory overhead or execution slowdown.

UPX is copyrighted software released under the GNU General Public License, with special exceptions that allow free use in commercial programs as outlined in the UPX License Agreement. This makes it suitable for both open-source projects and professional software distribution.

The application relies on the NRV compression library to deliver high-speed compression. An open-source alternative is available through the UCL compression library, offering compatibility for users who prefer fully open implementations.

UPX Features:

• Excellent compression ratio: typically achieves higher than WinZip, Zip, and Gzip. Use UPX to decrease the size of your distribution!
• Very fast decompression: ~10 MB/sec on an ancient Pentium 133, ~200 MB/sec on an Athlon XP 2000+.
• No memory overhead for your compressed executables because of in-place decompression.
• Safe: you can list, test, and unpack your executables. Also, checksums of both the compressed and uncompressed files are maintained internally.
• Universal: can pack several executable formats.
• Portable: UPX is written in portable endian-neutral C++.
• Extendable: thanks to its class structure, new executable formats or compression algorithms can be added easily.
• Free: Distributed with full source code under the GNU General Public License v2+. Free use in commercial programs is allowed through special exceptions stated in the License Agreement.