Three devices that are contained inside the computer case.

The most important component in the case is the central processing unit (CPU), also called the processor or the microprocessor.
The largest and most important circuit board in the computer is the motherboard, also called the main board, the system board. The mother board contains a socket to hold the CPU, where most of the processing takes place.
A power supply with power cords supplying electricity to all devices inside the case.