Installation (computer programs)

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Installation (or setup) of a program (including drivers, plugins, etc.) is the act of putting the program onto a computer system so that it can be executed.

Some software can be executed by simply copying it to a computer and executing it with no further ado; no installation procedure as such is required. Other programs are supplied in a form not suitable for immediate execution, and require an installation procedure. Installation may include unpacking of files supplied in a compressed form, copying them to suitable locations, tailoring the software to suit the hardware and the user's preferences, providing information about the program to the operating system, and so on. The installer may test for system suitability and available mass storage space.

Because the requisite process varies for each program and each computer, many programs (including operating systems) come with a general-purpose or dedicated installer – a specialized program which automates most of the work required for their installation.

Some software is designed to be installed simply by copying their files to the desired location, and there is no formal installation process. This was once usual for many programs running under MS-DOS, Mac OS, Atari TOS, AmigaOS since early versions of these operating systems and actually it is very common and "de facto" standard in Mac OS X applications and is also used for many Windows applications. There are versions of some operating systems which do not themselves require installation, and can be run directly from a bootable CD, DVD, or USB drive, without affecting other operating systems installed (but not running) on the machine. Examples are AmigaOS 4.0, Knoppix Linux, MorphOS AmigaOS clone, or Mac OS 1-9.

Common operations performed during software installations include creation or modification of:

Shared and non-shared program files
Folders/directories
Windows registry entries (Windows only)
Configuration file entries
Environment variables
Links or shortcuts

1 Some jargon expressions
2 Installer
- 2.1 Bootstrapper
- 2.2 Common installers
3 See also
4 References
5 External links

Some jargon expressions

Silent installation: Installation that does not display messages or windows during its progress. "Silent installation" is not the same as "unattended installation", though it is often improperly used as such.

Unattended installation

Installation that is performed without user interaction during its progress or, in a stricter sense, with no user present at all, except eventually for the initial launch of the process. An installation process usually requires a user who "attends" it to make choices at request: accepting an EULA, specifying preferences and passwords, etc. In graphical environments, installers that offer a wizard-based interface are common. However these installers may also provide command line switches that allow performing unattended installations.

Answer file: Some unattended installations can be driven by a script providing answers to the various choices such as the answer file which can be used when installing Microsoft Windows on a large number of machines.

Self installation: Unattended installation, without the need of initial launch of the process (i.e. Vodafone Mobile Connect USB Modem or Huawei E220's Mobile Partner software that self-installs from the USB port).

Headless installation: Installation performed without using a monitor connected to the destination computer (in particular, on a computer with no video output at all). This can be an (attended) installation performed from another machine connected via LAN or via a serial cable.

Unattended and headless installations are common tasks for system administrators.

Clean installation: Given the complexity of a typical installation there are many factors that may interfere with its successful completion. In particular files that are leftover from old installations of the same program or an unstable situation of the operating system may all act to prevent a given program from installing and working correctly. An installation performed in absence of such interfering factors (which may vary from program to program) is called a clean installation. In particular, a clean operating system installation can be performed by formatting its destination partition before the actual installation process.

Flat installation: An installation of a program performed from a copy (called a flat copy) of its original media contents (mostly CDs or DVDs) to a hard drive, rather than directly from the media. This may help in some situations where the target machine isn't able to cope with random access reads from CD/DVD at the same time as performing the CPU-intensive tasks often required by an installation, or where the target machine does not have an appropriate physical drive.

Network Installation: An installation of a program from a shared network drive. This may simply be a copy of the original media (as in a Flat Installation), but frequently, software publishers which offer site licenses for institutional customers provide a version intended for installation over a network.

Virtual installation: AmigaOS features a centalized standard installation utility called Installer since version 2.0 in 1991. It is driven by a LISP language interpreter, and users have the faculty of editing the installation scripts as these are plain text files. Installer also features the unsurpassed chance for users to perform virtual installations and verify any possible problem before committing the real installation.

Installer

An installation program or installer is a computer program that installs files, such as applications, drivers, or other software, onto a computer. Some installers are specifically made to install the files they contain; other installers are general-purpose and work by reading the contents of the software package to be installed.

The differences between a package management system and an installer are:

Package Management System	Installer
Typically part of the operating system.	Each product comes bundled with its own installer.
Uses a single installation database.	Performs its own installation, sometimes recording information about that installation in a registry.
Can verify and manage all packages on the system.	Only works with its bundled product.
Single package management system vendor.	Multiple installer vendors.
Single package format.	Multiple installation formats.

Bootstrapper

During the installation of computer programs it is sometimes necessary to update the installer or package manager itself. To make this possible, a technique called bootstrapping is used. The common pattern for this is to use a small executable file (e.g. setup.exe) which updates the installer and starts the real installation after the update. This small executable is called bootstrapper. Sometimes the bootstrapper installs other prerequisites for the software during the bootstrapping process too.

Common installers

A currently popular format for Microsoft Windows is the MSI installation package, which is installed by Windows Installer. Companies making tools for creating installers for Windows include Flexera Software's InstallShield, JExpress, InstallBuilder, Wise, Actual Installer ^[1], Smart Install Maker ^[2] and ScriptLogic Corporation (Formerly MaSaI Solutions). Most of these tools can create MSI packages as well as their own proprietary executables.

Free alternatives include NSIS, Clickteam, InnoSetup and a tool from Microsoft called WiX. Java projects will also be interested in the open source IzPack which allows generation of cross-platform installers.

Mac OS X has an application called Installer bundled with it. However, this is not technically an installer (see table above), but a Package Manager. Some commercial applications for Mac OS X use a custom installer, often Installer VISE or Stuffit InstallerMaker. Applications that do not need to install additional system components can be installed by moving the application files to a desired location on a hard drive; this is known as drag-and-drop installation and no installer software is needed. Mac OS X also includes a separate software updating application, Software Update (also known by its shell command, softwareupdate) but only supports Apple and system software.

An installation program on a CD is often designed to run automatically when inserted into the optical disc drive.

As a compromise between the Windows installer concept and the package management systems of UNIX-like systems, Windows installation management systems exist. Many of these form a part of systems management software, and (in some cases open source) alternatives exist to these.