Internal system unit components: specialized cards eg network, graphic cards

Specialised cards can be added to a system.

The graphics components are the part of your computer that control and enhance how graphics (pictures, videos, programs, animation, 3D) are displayed on your computer screen

A Network interface card, NIC, or Network card is an electronic device that connects a computer to a computer network, usually a LAN. It is considered a piece of computer hardware. Today, most computers are equipped with network cards.

The function of these components are to give people access to different things depending on the purpose of the card for example;

you could have a sound card. Its purpose is to make sound.
A video card’s purpose is to display video on your monitor.
A TV tuner card records television.
A DAC card gives control voltage to external devices.