A PC computer is a modular type of computer, it can be assembled using hardware components made by different manufacturers, so as to have a custom built computer according to one's specific needs.
The casing: metal casing which houses the internal components of the computer. The casing usually comes with it's own power supply and a set of screws, connectors and cables.
The motherboard: a large printed circuit board used to connect the processor, RAM, hard drives and CD/DVD drives, and comes with its own set of riser connectors.
The processor: the computer's main integrated circuit, the true brain of the computer, performing all the main calculations.
Storage devices such as hard drives, CD-ROM and DVD-ROM drives and burners, and the floppy disk drive.
Expansion cards are used to upgrade computer functionality and performance.