Installation (computer programs)

Installation (or setup) of a computer program (including device drivers and plugins) is the act of making the program ready for execution. Installation refers to the particular configuration of software or hardware with a view to making it usable with the computer. A soft or digital copy of the piece of software (program) is needed to install it. There are different processes of installing a piece of software (program). Because the process varies for each program and each computer, programs (including operating systems) often come with an installer, a specialised program responsible for doing whatever is needed (see below) for the installation. Installation may be part of a larger software deployment process.

Installation typically involves files containing program code and data being copied/generated from the installation to new files on the local computer for easier access by the operating system, creating necessary directories, registering environment variables, providing a separate program for un-installation etc. Because program files are generally copied/generated in multiple locations, uninstallation usually involves more than just erasing the program folder. For example, registry files and other system code may need to be modified or deleted for a complete uninstallation.

Some computer programs can be executed by simply copying them into a folder stored on a computer and executing them. Other programs are supplied in a form unsuitable for immediate execution and therefore need an installation procedure. Once installed, the program can be executed again and again, without the need to reinstall before each execution.

Common operations performed during software installations include:

Some installers may attempt to trick users into installing junkware such as various forms of adware, toolbars, trialware or software of partnering companies. To prevent this, extra caution on what exactly is being asked to be installed is needed. The installation of additional software then can simply be skipped or unchecked (this may require the user to use the "custom", "detailed" or "expert" version of the installation procedure).

Such malicious conduct is not necessarily a decision by the software developers or their company but can also be an issue of external installers such as the Download.com installer by CNET.

Some computer programs need no installation. This was once the standard for 8-bit and 16-bit systems where software was run from floppy disc and only a single application could be loaded at once, such as on the Apple II, PET, MS-DOS, and Macintosh 128K. As computing environments grew more complex and fixed hard drives replaced floppy disks, the need for tangible installation presented itself. For example Commodore released the Installer for Amiga.

The modern applications that can be run without going through formal process of installation and, in particular, do not require modifications of the operating system, are sometimes referred to as zero-install. Zero-install can be achieved through multiple means: