A computer system in contemporary usage refers to a desktop system, including the computer itself (aka "The CPU" or "The Box") and all the peripheral devices needed to operate it, usually including:
The computer, usually mounted in a tower (vertical) case, including components: the CPU or central processing unit; a mother board or mainboard, including a BIOS; A graphics card; a sound card (often build onboard, ie. into the mainboard), a variety of disk ports to serve hard drives, disk drives and optical drives, a variety of peripheral ports, including USB ports, legacy serial and parallel ports, legacy psx, and SCSI; and LAN ports, either ethernet or firewire. A hard drive (sometimes more) is included for long-term data storage. The case also contains a transformer power supply and a number of fans to keep the internal components cool while operating.
A monitor, typically either a CRT or an LCD flatscreen.
A set of speakers to hear sound.
A keyboard, typically a standard 104-key QWERTY keyboard.
A mouse, typically a three button mouse with scroll wheel.
