several layers, printed cuircuit board.
(also called interface cards, adapter cards) are circuit boards (small motherboards), which are put into the expansion slots in the motherboard. Examples:
Newer motherboards may already include video and sound functions.
=points where a peripheral device is plugged into the system unit. Connectors (which may be male or female) are what you plug into the port. Ports can be serial (one bit at a time) or parallel (many bits at a time, faster but less reliable, used for printers, for instance). Some often used ports are:
for transfering data, consist of data bus (for transmitting data) and address bus (for information where to find the data). The bus width tells how many bits can travel per time unit, the number of time units per second of the bus is measured by the clock speed.
between CPU and memory
connection to peripheral devices.