In computing, an input device is a piece of computer hardware equipment used to provide data and control signals to an information processing system such as a computer or information appliance. So, it is not a function of an operating system.

Introduction:
An operating system (OS) is a software that manages computer hardware and software resources and provides common services for computer programs. It acts as an interface between the user and the computer system, controlling and coordinating the various hardware and software components to ensure efficient operation. While the OS performs several functions, one of them does not involve supplying input.

Explanation:
The functions of an operating system can be categorized into several categories, such as interface, resource management, process management, memory management, file management, and device management. Let's discuss each of these functions in detail:

1. Acting as an interface:
An operating system acts as an interface between the user and the computer system, providing a user-friendly environment to interact with the computer. It allows users to execute commands, run applications, access files, and perform various tasks easily.

2. Supplying input:
This option is incorrect as an operating system does supply input. The operating system receives input from the user through input devices such as a keyboard, mouse, or touchscreen. It processes this input and performs the necessary actions based on the user's instructions.

3. Controlling devices:
An operating system controls and manages various hardware devices connected to the computer system. It provides device drivers that enable the communication between software applications and hardware devices such as printers, scanners, network cards, etc.

4. Managing memory:
Memory management is an important function of an operating system. It allocates and manages the computer's memory resources efficiently, ensuring that each program and process gets the required memory space. It also handles memory swapping, virtual memory management, and memory protection.

Conclusion:
In conclusion, an operating system performs several functions to ensure efficient operation of a computer system. While it acts as an interface, controls devices, and manages memory, it does not supply input. The operating system receives input from the user through input devices and processes it accordingly.