why is program installation a process?

this may very well be a stupid question, but when i was asked something much simplier then this, i didn't have much of an answer...

why are most programs installed via some several step process of adding and changing and whatnot? we have programs that can be ran straight from a self contained executable, but a large portion of programs cannot. why is this? is it due to the progr开发者_Go百科ams growing exponentially by needing to include everything within itself? if that is the case, it is so difficult to design an OS from the ground up to be completely modular... ie. having an OS with a standard set of modules, that can be accessed and used from any 'standalone program' that doesn't require a lengthy install.

thanks David Kirsch.

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It's really a question of how complicated your program is. Many windows programs have dependencies on Visual Studio C++, .Net, Java etc. runtimes that are not delivered by the substrate OS. This means that for your programs to work those components must already be on the system.

If those prerequisites are missing, then your program won't even load, so you can't even get your program to check for them and tell the user to go and get them. This is where an installer comes in, as it generally doesn't have any prerequisites, but is able to sniff out the ones your progam needs and can either tell you to go and get them, or try to install them for you.

Also many programs need some logical, as well as physical, installation work to be done as part of deployment. This might mean registry changes (such as COM registration), changes to IIS (setting up a web application and virtual directory), or changes to the Service Control manager (setting up Windows Services).

In short, unless your program is extremely self-contained and has no external dependencies, an installer is the only way to get your application on the desktop.