A computer is composed of multiple components that perform specific functions. In many computers, a component may be replaced independently without replacing the other components. This allows only a specific part to be replaced as the item breaks down or becomes obsolete.
The motherboard provides connections for all the peripheral (child) devices. It's becoming increasingly common for a motherboard to perform these peripheral functions without a separate device.
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Central Processing Unit
The central processing unit (CPU) is the "brain" of the computer and performs most of the actual computing functions. The CPU determines how quickly the computer can perform most tasks.
The hard drive provides the permanent storage for information. This information is still recorded when the computer is turned off.
The memory card holds information temporarily while the computer is turned on. The retrieval and storage of memory is much faster than that of the hard drive.
The monitor is similar to a television and displays visual information to the user.