Installation is the process of putting a program in a computer system such that the program works as desired. It includes configuration. However, further configuration changes may be made once a program is installed. Ideally, such changes are made only if the demands on that program change.
An installer is a program that installs another one. Either such a program or a person can carry out an installation. The latter is known as a manual installation.
Some operating systems are pre-installed. This means that computers are supplied with the installation already completed. Other ones don't need to be installed on a hard disk, for example Knoppix Linux, and can be run from a bootable CD without affecting existing installed operating systems.
The installation of a program generally adds the following components to the computer's file system