UPX 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.
excellent compression ratio: typically compresses better than WinZip/zip/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, 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.
What´s New in version 3.91:
experimental support for Win64/PE
FreewareFiles tested UPX (Ultimate Packer for eXecutables) 3.91 on 2013-10-01 using leading
antivirus scanners and found it 100% Clean. It does not contain any form
of malware, spyware, viruses, trojans, etc. We will re-test each updated
version and remove the award as well as the program if found infected.