Programs make the computer into a particular machine.
Every different program makes it into different machine.
The program code that feeds the computer is coded binary numbers. The size of the code depends on the bit size of the computer. The task of the program is to move numbers from register to register and do logic or arithmetic with them. Nor can you write much program that talks to the computer. There are however microcontrollers, small, single chip computers that you can program in their native language.