note11 - CSCI 120 Introduction to Computation Ports and I/O...

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Unformatted text preview: CSCI 120 Introduction to Computation Ports and I/O devices (cont.) (draft) Saad Mneimneh Visiting Professor Hunter College of CUNY 1 Input devices An input device is any hardware component that allows users to enter data (programs, commands, and user responses) into a computer. Depending on the application and the particular requirements, the input device selected may vary. 1.1 Keyboard This is the most basic input device. The keyboard contains keys users press to enter data into a computer. Desktop computer keyboards typically have from 101 to 105 keys. Keyboards for smaller computers, such as laptops, contain fewer keys. All computer keyboards have a typing area that includes the letters of the alphabet, numbers, punctuation marks, and other basic keys. The keys orig- inally were arranged to reduce the frequency of key jams on old mechanical typewriters. The first six letters on the top alphabetic line spell QWERTY, thus giving the name QWERTY keyboard. A DVORAK keyboard, by contrast, places frequently typed letters in the middle of the typing area. Despite the logical design of a DVORAK keyboard, all keyboards today are QWERTY. Many keyboards also have a numeric keypad on the right side of the key- board, two CTRL keys, two ALT keys, a set of arrow and additional keys between the typing area and the numerical keypad, and twelve function keys (enhanced keyboard). The command associated with a function key may vary, depending on the program with which we are interacting. 1.2 Pointing devices A pointing device is an input device that allows a user to control a pointer on the screen. In a graphical user interface, such pointer is usually a small symbol whose location and shape change as a user moves the pointing device. A pointing device can be used to move the insertion point of typed text, select a portion of the text, select graphics, click buttons, icons, links on a web page, and menu commands. 1.2.1 Mouse The mouse was invented by Douglas Engelbart in 1964 and was refined by Xerox and employed for the first time with Apple Macintosh computer in 1970s. It was mass produced in the mid 1980s. It is now the most widely used pointing device. With a mouse, the user controls the movement of the pointer, often called the mouse pointer in this case. The mouse pointer moves on the screen mimicking the mouse movements. The mouse has buttons that can be clicked once the mouse pointer is at the desired spot, to perform various actions. GUI driver operating system I/O controller driver I/O controller Figure 1: This shows how the mouse can control the pointer on the screen. The operating system (OS) is a software program that is continuously running to coordinate the activity of the whole machine, e.g. Windows; for instance, its the OS that loads other programs in memory. The OS has a number of components among which are the Graphical user interface (GUI) and drivers for I/O controllers....
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This note was uploaded on 03/27/2010 for the course CSCI 120 taught by Professor Saadmneimneh during the Spring '09 term at CUNY Hunter.

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note11 - CSCI 120 Introduction to Computation Ports and I/O...

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