What is the difference between copying a program into the system and installing a program into a system?

Answer 1

In some (not many) cases there is no difference. Installing the program is nothing more than creating a folder in "Program Files", copying the software into that folder and creating a shortcut to the .exe either on your start menu or on the desktop.

For most programs though if you did that it simply wouldn't work.

Most programs that have installation software (usually called setup.exe) go though a more complex process. This involves creating various entries in the windows registry, placing .dlls that are needed somewhere in the windows folder, perhaps creating various drivers in windows folders where they will be needed, creating file associations as well as doing the straightforward copying and shortcut creation mentioned above. If the software requires a license or serial number then there will be a user prompt for that and the result will be encrypted and hidden away somewhere. Furthermore, since exactly how this all works will depend on which operating system you have installed and what your system configfuration is like there will be some code that scans your system and performs the install according to what it finds.

Unfortuantely this means that once something is installed you cannot move it (to a different drive or different computer) with a simple copy and paste. It has to be reinstalled and the whole process repeated.