What is the main function of a 'compiler'?

The primary role of a compiler is to translate source code written in a high-level programming language into machine code that a computer's processor can execute directly. This function is crucial because high-level languages are designed for ease of understanding and writing by humans, but the machine's hardware requires instructions in binary format. By converting the high-level code into machine code, a compiler enables the software written by developers to be run efficiently on a computer.

Other choices do not accurately describe the core purpose of a compiler. Providing a user interface pertains to the design and interaction aspects of software applications, while enhancing security generally relates to measures taken to protect code from vulnerabilities, such as encryption or access controls. Testing compatibility involves checking if software works correctly across different systems or environments, which is not the function of a compiler.