Why some applications need first to be “installed” in order to run while others don't?

Question

Why some applications need first to be "installed" in order to run while others don't?

Applications like Adobe software all need to be first installed on Windows before they can be run, but some other applications simply don't need any installation, Why?

Answer 1

There are plenty of reasons that may require an application to be installed:

1. System services
2. Registry usage - for application-specific settings, or settings shared with other applications
3. Drivers - any access to hardware or unique access to network/bluetooth would require some sort of installation
4. Network interface
5. Discovery - some applications provide services that can be used by other applications or the OS (think COM, .Net etc.)

Answer 2

Many programs send 'roots' into the OS, providing increased functionality for the program. Installation is what creates this functionality by changing the registry.

Other programs are designed to be portable or lightweight, and therefore avoid using the registry.

So the difference can be looked at as the difference between a tree planted in the ground, and a tree in a pot. The tree in the ground will grow large and strong, but can't be moved easily.

The tree in a pot will never get very large or do much, but it can be moved around wherever it needs to go.

Answer 3

There are many application that write data to the registry. Everything from the location of files that it needs to load to start up, to saved data etc. If that data is not written, then when it tries to access a non-existent registry key, it crashes.

In addition, many times an installer contains a package that needs to be unpacked. You download one file, but the program wants folders, many files etc. This also sometimes needs to be done before the program can be used.