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both are called peripheral units or devices through which the computer communicates with the outside world, as the systems that store or archive information, serving as auxiliary memory from main memory.
means any set of peripheral devices that do not belong to the core of the computer, made by CPU and main memory , allow perform operations I / O (E / S) complementary to the data processing performed the CPU. These three basic units in a computer, CPU, main memory subsystem and the E / S, are connected via three buses or channels of communication: the address bus to select the address of the data or peripheral to that want to access, control bus, basically to select the operation to be performed on the data (mainly reading, writing or modification) and the data bus, along which the data.
Although the term often involves peripheral concept of "additional but not essential" many of them are essential to a computer system. The keyboard and monitor, essential in any personal computer today (they were not in the first computers) are probably the most common peripherals, and many people may not consider them as such because they generally are taken as necessary part of a computer. The mouse is probably the clearest example of this. Less than 20 years ago, not all personal computer including this device. The MS-DOS operating system, the most common at the time, had a command line interface for that was not necessary the use of a mouse, it was all done through commands text. It was with the popularity of Windows when the mouse started to be an essential element in any home equipped with a personal computer. Currently there are operating systems with text interface also makes use of the mouse, for example, some systems UNIX and LINUX