Input and Output
Three important features generally characterize the interaction of a computer system with its users: input, processing, and output. Input and output (sometimes referred to as input/output or simply I/O) refers to the transfer of information back and forth within a computer system. Individually, input involves the information that is gathered and entered into the central processing unit (CPU) for processing, and output involves the information that is subsequently processed through the CPU and exited so that it can be made available (and useful) to computer users.
Information that is considered input can take a variety of forms, such as commands from a user at a keyboard (sometimes with the help of a mouse), information from another computer or device, or information from a file stored on a disk drive. Devices that help to input data into the computer are generically called "input devices." Some input devices are operated directly by the user (e.g., keyboard, mouse, touch screen, and joystick), while others are sensors or transducers that convert (usually analog to digital) external signals into data (e.g., microphone).
Information that is referred to as output is considered the result of processing the input information, whether the resulting data is sent to a monitor screen or printer, stored as a file on a disk, or sent to another computer on a network. The output can also vary from meaningful to unintelligible data; where in the later case error messages often result. Electronic or electromechanical equipment connected to a computer that help to transfer data out of the computer are generally named "output devices" (such as a display screen, printer, CD-ROM (compact disc-read-only memory) driver, fax machine, scanner, and set of speakers). Such devices traditionally move data out in the form of text (e.g., printed pages), images (e.g., pictures), sounds (e.g., music), or by other means.
Certain devices are considered both input and output devices ("I/O devices"), such as a disk drive, magnetic tape drive, diskette, and CD-RW (compact disc-rewriteable), because they can provide unprocessed input information to the computer, as well as receive processed output data from the computer. Therefore, while an input device always sends information "to" a computer and an output device always sends information "from" a computer, an I/O device is able to transfer information both "to" and "from" the computer. The circuitry that monitors operations and performs tasks relating to receiving input and transferring output at an input or output device is called the input/output controller.
Input and output activities are part of computer data processing, the analysis and organization of data by the repeated use of one or more computer programs. Nearly all business, engineering, and scientific organizations rely on the data processing of information for the various aspects of their operations. The input of raw information into computers are eventually output into useful data that can then be used for such tasks as personnel tracking, payroll preparation, accounting, record-keeping, inventory control, sales analysis, financial analysis, just to name a few.
The BIOS (Basic Input/Output System) is the program that manages dataflow between the computer's operating system and its attached I/O devices such as the hard disk and video adapter (for the monitor screen). When the BIOS starts ("boots") a computer, it first determines whether the attachments are properly connected and operational, and then it loads the operating system into the computer's random access memory (RAM). With the use of the BIOS, the operating system and its applications are relieved from dealing with the exact details about the attached input/output devices. When such details change, only the single BIOS program needs to be altered, and neither the operating system nor any applications are changed. Although the BIOS is generally the intermediary between the microprocessor and I/O devices with regards to dataflow, in some cases the BIOS can arrange for data to flow directly to memory from devices (such as video adaptors) that require faster dataflow in order to be effective.
The activity of echoing is an important part of the functions of input and output. Echoing is a signal that is transmitted back to the sender but is distinct from the original signal. The act of echoing permits the print or display of characters in several ways: (1) as they are entered from an input device, (2) as instructions are executed, or (3) as retransmitted characters are received from a remote terminal. Data circuits that are connected to computer programs are commanded to transmit received data back to the sending station by displaying data as it is received from the keyboard. By "echoing" a user is able to visually inspect what was received.
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