Which one of the following is commonly referred to as the brain of any computer system ?

The Central Processing Unit (CPU) is widely known as the "brain" of any computer system. It is the primary component responsible for interpreting and executing most of the commands from the computer's hardware and software. The CPU performs all basic arithmetic, logical, control, and input/output (I/O) operations specified by the instructions.

The CPU itself consists of two main sub-components: the Arithmetic Logic Unit (ALU), which performs mathematical calculations and logical comparisons, and the Control Unit (CU), which directs the flow of data and instructions. While the ALU and CU are vital, the CPU as a whole is the integrated unit that manages the system's operations. An Application Server is a software framework or hardware device that provides an environment for applications to run, rather than being a core processing component of a computer's architecture.