Also called a "setup program," it is software that prepares an application (software package) to run in the computer. Typically combined with the application it is installing, the install program creates a folder with a default name on the hard disk and copies the application files to that folder. The complete installation package is either an Internet download or on a CD-ROM, DVD-ROM or possibly a diskette. Application files are generally compressed in the package, and the install program decompresses them into their original format and respective folders.

With Windows applications, the install program often adds or updates extensions to Windows that reside in the Windows folder (see DLL hell). It is also customary for the install program to deposit an uninstall option so the application can be easily removed later on (see uninstall).

Also Used for Hardware
Install programs are also used to attach a new peripheral device to the computer. The install program may add the device's driver to the operating system, or it may be used to set or reset parameters in an updatable memory (flash memory, EEPROM, etc.) on the expansion board that was just plugged in. See uninstall, how to install a program and BIOS setup.