The term "computer" is derived from the Latin word aggregate computare -. A computer consists of always the same components: input devices, computer and output devices. They operate on the principle known as EVA. This means input processing output. According to this principle all work computer. Even a small mini-computer that controls the VCR, works on this principle. The input is done via the remote control, the software of the processing unit (CPU) processes the commands and specialized output devices to control the VCR. There are two principles of computers: analog and digital computers. In the analog voltages to be added or subtracted, as 2 V + 2 V = 4 volts. These computers could not penetrated, it will use only the digital computer. This principle of numbers and letters in the digital dual-system converted and then processed. In the o.g. Example is digitized, the number 2, from 2 OOIO. Mathematically, the whole looks like this: + OOIO OOIO = OIOO (4).

In the 1970s it has started the development of computers for personal purposes. The term PC (personal computer) was born. The first industrially produced PC was the Apple II, which was presented to 1977th In 1981, IBM has done with its first IBM-PC a breakthrough. After that we went with the development and sale of PC's steep upward. Today, there are no longer applicable not likely to be carried out by a PC. The hardware and software is at a very high technical standard is also in the personal computer is the EVA-principle. As input here next keyboard or mouse, scanners, graphic tablets, cameras, their place. Output devices are modern TFT displays, projectors, printers and plotters. The processing unit has processed more than enough computing power and storage capacity for even complex data, as they appear in pictures and movies.

The mainframe is designed by its design to a high reliability and processing power. Unlike a personal computer to a mainframe several people are working simultaneously or it can be handled large amounts of data. These special computers are therefore particularly suitable for banks, insurance companies, large companies and administrations. In air-conditioned rooms that are operated in so-called mainframe data centers. This type of computer needs a high energy and therefore produce a relatively large amount of waste heat. Such activities need to be air-conditioned data centers. Another advantage of the mainframe's virtualization of multiple small servers. With special operating here a variety of virtual server is started. Thus, space, power and administration savings. An example of the use of virtual server is the Internet. Any website which requires a server for your applications can run on a virtual server.

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