Explanation:

- Option 1: Compiler

- Translates code written in a high-level programming language into machine code. It does not control the computer system.

- Option 2: Operating System

- A collection of programs that manages the hardware, software resources, and provides common services for computer programs. It controls how the computer system runs and processes information.

- Option 3: Linker

- Combines multiple object files into a single executable and resolves references between them. It doesn't control the system.

- Option 4: Assembler

- Converts assembly language into machine code. It's a tool, not a system controller.

Correct Answer: Option:2 i.e. Operating System