The brain of the computer is the Central Processing Unit (CPU). The CPU is responsible for executing instructions and performing calculations in a computer system. It is often referred to as the "brain" or "heart" of the computer because it controls and coordinates all the other hardware components.

The CPU consists of several key components that work together to carry out the processing tasks. These components include:

1. Control Unit: The control unit is responsible for fetching instructions from the computer's memory, decoding them, and executing them. It controls the flow of data and instructions within the CPU and coordinates the activities of other hardware components.

2. Arithmetic and Logic Unit (ALU): The ALU performs arithmetic operations (such as addition, subtraction, multiplication, and division) and logical operations (such as comparisons and boolean operations). It is the core component where actual calculations and logical operations take place.

3. Registers: Registers are small, high-speed memory units located within the CPU. They are used to store data, instructions, and intermediate results during processing. Registers provide quick access to data, reducing the need to access the computer's main memory.

4. Cache: Cache is a small, high-speed memory located inside the CPU. It stores frequently accessed data and instructions to reduce the time it takes to fetch them from the computer's main memory. Cache memory helps improve the overall performance of the CPU by providing faster data access.

The CPU works in conjunction with other hardware components, such as memory and input/output devices, to carry out the instructions and perform calculations. It fetches instructions from the computer's memory, decodes them, and then executes them by performing the necessary calculations or operations.

In summary, the CPU is considered the brain of the computer because it controls and coordinates all the activities within the computer system. It carries out the processing tasks by fetching instructions, performing calculations, and executing operations.