Explanation:
The main circuit board (physical component) of a computer system is the motherboard. It is the backbone of the computer system, connecting all the hardware components together, including the central processing unit (CPU), memory, storage devices, and other peripherals. The motherboard also contains slots for expansion cards, such as graphics cards, sound cards, and network cards.

Functions of a Motherboard:
The motherboard performs several critical functions in a computer system, including:

1. Providing power and communication pathways: The motherboard regulates the power supply to all the other components in the system and provides communication pathways between them.

2. CPU support: The motherboard contains a socket or slot for the CPU, which is the brain of the computer. The CPU communicates with other components through the motherboard.

3. Memory support: The motherboard provides slots or sockets for memory modules, which are used to store data and instructions for the CPU.

4. Expansion slots: The motherboard provides expansion slots for additional hardware components, such as graphics cards, sound cards, and network cards.

5. Peripheral support: The motherboard provides connectors for peripherals, such as USB ports, audio jacks, and Ethernet ports.

Conclusion:
In conclusion, the motherboard is the main circuit board of a computer system, responsible for connecting and communicating with all the other hardware components. It is a critical component that provides power and support for the CPU, memory, expansion cards, and peripherals.