Final answer:
The I/O cards are housed within the system unit or computer case, specifically in the expansion slots on the motherboard.
Step-by-step explanation:
The component that houses the I/O cards is known as the system unit or computer case. Typically, the system unit includes several bays and slots where various internal components are installed. One of the key features of the system unit is its expansion slots on the motherboard, where I/O cards, also known as expansion cards, can be inserted.
These expansion cards provide additional functionality to a computer, such as improved video rendering capabilities through a graphics card or enhanced audio features through a sound card. The back of the system unit is where these cards often connect to external devices, with ports that are accessible from the outside for users to plug in peripherals.