Elements of hardware

Computer hardware is the electronic part of the com­puter that stores and manipulates symbols under the direction of the computer software. Because the hardware's operations are electronic, the computer is both fast and accurate. The speed of many operations performed within the computer is limited only by the speed of electricity. These operations also obey physical laws that do not change from operation to operation and are therefore accurate. If you will recall, a computer mistake can almost always be traced to a human error, either in the design of the computer or in the software.

To understand how the computer hardware is combined to make a machine, that stores and manipulates symbols, we first look at a conceptual computer, which can demonstrate the major functions of a computer without involving the operational details of the machine. The conceptual computer has four major elements: input, processing/internal memory, secondary stor­age, and output.

A computer must be able to input, or receive, the data to be manipulated and the software instructions for manipulating those data. Input to a computer performs the same function as the input humans receive through sight, hearing, touch, taste, and smell.

Once the data and instructions are input, the computer must be able to store them internally and then process the data based on the instructions. This storage and processing, which occurs in the processing/internal memory unit, can involve many different types of operations, including arithmetic operations (addition, subtraction, and so on) on numbers, operations on letters of the alpha­bet, and operations that result in pictures (known as graphics). The processing/ internal memory unit is comparable to the human brain, which also stores and operates on data. In the PGE example, the PC processes the weather data to check them for reasonableness and to prepare them for further processing by the mainframe.

Because the internal memory of a computer does not have an unlimited capacity, a storage area is needed outside of the computer to hold the data and information, which can be brought back into the internal memory as needed. This external storage unit is called secondary storage. Another reason for hav­ing secondary storage is that the computer's internal memory is erased when the power to the computer is turned off. Anything in internal memory that must be saved before the power is turned off should be transferred to secondary storage. The file cabinets we use to save large amounts of data and information are anal­ogous to a computer's secondary storage.

Finally, because the processed information is of no use unless it is pro­vided to the user, the computer has a process called output. We humans output the results of our brains' operations in the form of speech, writing, pictures, or body movements. In the PGE example, output from the PC is in an electronic form that is sent directly to the mainframe, where it is processed and output as printed reports.

We have looked at a conceptual computer and have discussed the parts of a computer in general terms. We have also seen how the input of data into the computer, the flow of data and information between the computer and secondary storage, and the output of information from the computer link the components of the conceptual computer together. Before we discuss further how a computer works, we should look at the four major parts of a real computer. After reading this section, you should have a clear idea of the main components of a computer.

Input

The many methods of input to a computer range from grocery checkout bar codes to easy-to-use voice input. Currently, the most popular form of input is the typewriter like keyboard, which sends the appropriate electrical signal to the computer when the user presses a key. The symbol corresponding to this key is stored in the computer's internal memory and usually is shown simultaneously on the screen.

Other common forms of input include the joystick used for games and a device called a mouse that communicates with the computer when the user moves it over a flat surface and presses one or more buttons. Touchscreens that transmit a signal to the computer based on what part of the screen is touched are used in various situations, as are light pens that the user points at a portion of the screen to select it for further investigation. Touch screens provide infor­mation to visitors all over EPCOT Center at Walt Disney World in Florida. A visitor merely touches one of several colored areas on the screen to receive a message about a feature of EPCOT. The newest forms of input are pen-based computing and voice recognition. In the former case, the user writes on the screen; in the latter case, the user speaks to the computer.

Дата добавления: 2015-11-14