UPX 3.94 (Ultimate Packer for eXecutables)


UPXUPX (Ultimate Packer for eXecutables) is a free, portable, extendable, high-performance executable packer for several different executable formats. It achieves an excellent compression ratio and offers very fast decompression. Your executables suffer no memory overhead or other drawbacks because of in-place decompression.

UPX is copyrighted software distributed under the terms of the GNU General Public License, with special exceptions granting the free usage for commercial programs as stated in the UPX License Agreement. This software uses the NRV compression library for compression services. A compatible but somewhat less efficient OpenSource implementation is available through the UCL compression library.

Strengths in a nutshell:

  • Excellent compression ratio: typically compresses better than WinZip/zip/gzip, use this application 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, a checksum of both the compressed and uncompressed file is maintained internally.
  • Universal: UPX can pack a number of executable formats.
  • Portable: UPX is written in portable endian-neutral C++
  • Extendable: because of the class layout it’s very easy to add new executable formats or new compression algorithms
  • Free: Distributed with full source code under the GNU General Public License v2+, with special exceptions granting the free usage for commercial programs as stated in the License Agreement.

Changes in UPX 3.94:

  • Add support for arm64-linux (aka “aarch64”).
  • Add support for –lzma compression on 64-bit PowerPC (Thierry Fauck).
  • For Mach, “upx -d” will unpack a prefix of the file (and warn).
  • Various improvements to the ELF formats.
  • Bug fixes


Size: 410 KB

Download Win32 version

Download Linux/i386 version

Download Linux/AMD64 version

Download WinCE/ARM version

Download DOS version

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