Computer hardware
Computer hardware is the physical part of a computer, including the digital circuitry, as distinguished from the computer software that executes within the hardware. The hardware of a computer is infrequently changed, in comparison with software and data, which are "soft" in the sense that they are readily created, modified or erased on the computer. Firmware is a special type of software that rarely, if ever, needs to be changed and so is stored on hardware devices such as read-only memory (ROM) where it is not readily changed (and is, therefore, "firm" rather than just "soft").
Most computer hardware is not seen by normal users. It is in embedded systems in automobiles, microwave ovens, electrocardiograph machines, compact disc players, and other devices. Personal computers, the computer hardware familiar to most people, form only a small minority of computers (about 0.2% of all new computers produced in 2003).
Motherboard
The motherboard is the "heart" of the computer, through which all other components interface.
* Central processing unit (CPU) - Performs most of the calculations which enable a computer to function.
o Computer fan - Used to lower the temperature of the computer; a fan is almost always attached to the CPU, and the computer case will generally have several fans to maintain a constant airflow.
* Random Access Memory (RAM) - Fast-access memory that is cleared when the computer is powered-down. RAM attaches directly to the motherboard, and is used to store programs that are currently running.
* Firmware usually Basic Input-Output System (BIOS) based or in newer systems Extensible Firmware Interface (EFI) compliant
* Internal Buses - Connections to various internal components.
o PCI 
o PCI-E
o USB
o HyperTransport
o CSI (expected in 2008)
o AGP (being phased out)
o VLB (outdated)
o ISA (outdated)
o EISA (outdated)
o MCA (outdated)
* External Bus Controllers - used to connect to external peripherals, such as printers and input devices. These ports may also be based upon expansion cards, attached to the internal buses.
o parallel port
o serial port
o USB
o firewire
Power supply
A case that holds a transformer, voltage control, and (usually) a cooling fan, and supplies power to the rest of the computer.
Storage controllers of IDE
Control hard disk, floppy disk, CD-ROM and other drives; the controllers sit directly on the motherboard (on-board) or on expansion cards, such as a Disk array controller.
Video display controller
Produces the output for the computer display. This will either be built into the motherboard or attached in its own separate slot (PCI, PCI-E or AGP), in the form of a Graphics Card.
See also:
Open hardware