UPX stands for Ultimate Packer for eXecutables. And that is what this program makes. With UPX you can pack executable files of many operating systems such as EXE, TOS or ELF files and compress them to a significantly smaller size. Nevertheless, the compressed files can be executed and run normally, what's a difference to a compression in RAR or ZIP format, where the files must be unpacked before you can execute them. In addition, UPX often achieves better compression rates than ZIP or RAR files, because UPX is specialized precisely to program files. For the user, there is no difference between a normal executable file and an UPX compressed executable file, because the unpacking program will be preceded before the packed program, so that it can decompress the application automatically.

Advantages

Advantages of this compression are primarily in the smaller file size (for example when downloading from the Internet) but also in a shorter loading time of the program (assuming decompressing takes less time than loading the file). Since files can be added to the packed executable, you can use this as another advantage.

Disadvantages

Some virus scanners detect UPX files as viruses, although they are not. In addition, under certain circumstances, other programs will not be able to access UPX compressed files because their structure has changed too much with the compression. Also, the decompressing can lead to unnecessary waste of system resources.

Supported Files

• Windows: EXE, DLL, OCX, BPL, CPL, SYS, AX, ACM, DRV, TLB
• DOS: COM, EXE, SYS, COFF
  
• Linux, NetBSD, OpenBSD: ELF, Kernel, PE, Shell Script, Generic
  
• Mac OS X/Darwin Executables
• Playstation 1 Executable PS1
• Atari TOS/MiNT
  

Windows Version with graphical user interface

Normally, UPX is a program that is operated via the command line. But for Windows, there is a UPX Program with a graphical user interface, that is portable and can be used without an installation.

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