environment ; ; ;
external environment
human-related ()
human-independent
remote terminal
reel of magnetic tape
input-output interface (, ) -
scan ; ;
scanner ;
bar-code scanner / bar-code reader -
regardless of ;
to match characteristics
similarly ; ;
to fall between ;
card reader ()
line printer ;
page printer
character printer
optical character reader
optical mark reader
visual display
digitizer - ;
keyboard input device
plotter
voice recognition and response unit
, - .
INPUT-OUTPUT ENVIRONMENT
Data and instructions must enter the data processing system, and information must leave it. These operations are performed by input and output (I/O) units that link the computer to its external environment.
The I/O environment may be human-related or human-independent. A remote banking terminal is an example of a human-related input environment, and a printer is an example of a device that produces output in a human-readable format. An example of a human-independent input environment is a device that measures traffic flow. A reel of magnetic tape upon which the collected data are stored in binary format is an example of a human-independent output.
Input-Output Interfaces, Data enter input units in forms that depend upon the particular device used. For example, data are entered from a keyboard in a manner similar to typing, and this differs from the way that data are entered by a bar-code scanner. However, regardless of the forms in which they receive their inputs, all input devices must provide a computer with data that are transformed into the binary codes that the primary memory of the computer is designed to accept. This transformation is accomplished by units called I/O interfaces. Input interfaces are designed to match the unique physical or electrical characteristics of input devices to the requirements of the computer system. Similarly, when output is available, output interfaces must be designed to reverse the process and to adapt the output to the external environment. These I/O interfaces are also called channels or input-output processors (IOP).
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The major differences between devices are the media that they use and the speed with which they are able to transfer data to or from primary storage.
Input-Output Device Speed. Input-output devices can be classified as high-speed, medium-speed, and low-speed. The devices are grouped according to their speed. It should be noted that the high-speed devices are entirely electronic in their operation or magnetic media that can be moved at high speed. Those high speed devices are both input and output devices and are used as secondary storage. The low-speed devices are those with complex mechanical motion or operate at the speed of a human operator. The medium-speed devices are those that fall between they tend to have mechanical moving parts which are more complex than the high-speed devices but not as complex as the low-speed.
High-speed devices: magnetic disk; magnetic tape.
Medium-speed devices: card readers; line printers; page printers; computer output microfilms; magnetic diskette; optical character readers; optical mark readers; visual displays.
Low-speed devices: bar-code readers; character printers; digitizers; keyboard input devices; plotters; voice recognition and response units.
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1. What is the purpose of input and output devices? 2. What types of input-output devices do you know? 3. Why are data transformed into a binary code while entering the input device? 4. Give an example of a human independent output. 5. What is an I/O interface? 6. What are the major differences between the
various I/O devices? 7. What types of I/O devices tend to be high-speed devices? 8. What types of devices tend to be low-speed devices?
4.
:
-; ; ; ; ; ; ; ; ; ; -; ; -; ; ; ; ; ; ; - ; ; ; ; ; .
5. , .
Environment: application environment; communication environment; execution environment; external environment; hardware environment; interface invironment; management environment; multimedia environment; network environment; processing environment; security environment; software environment; user environment.
Interface: channel interface; common interface; data interface; database interface; display interface; external interface; flexible interface; floppy-disk interface; general-purpose interface; hardware interface; low-level interface. Scanner: bar code scanner; black-and-white scanner; color scanner; desktop scanner; hand scanner; laser scanner; manual scanner; optical scanner; visual scanner.
Terminal: batch terminal; desktop terminal; display terminal; printer terminal; remote terminal; security terminal; logical terminal; text terminal.
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6. , , . :
The text / article under review...(gives us a sort of information about...) The article deals with the problem...
The subject of the text is...
At the beginning (of the text) the author describes... (dwells on...; explains...; touches upon...; analyses...; comments...; characterizes...; underlines...; reveals...; gives account of...)
The article begins with the description of..,, a review of..., the analysis of... The article opens with...
Then (after that, further on, next) the author passes on to..., gives a detailed (thorough) analysis (description), goes on to say that...
To finish with, the author describes... At the end of the article the author draws the conclusion that...; the author sums it all up (by saying...) In conclusion the author...
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As it is well known, a computer cannot perform or complete any useful work unless it is able to communicate with its external environment. All data and instructions enter and leave the central processing unit through primary storage. Input-output devices are needed to link primary storage to the environment, which is external to the computer system. So input devices are used to enter data into primary storage. Output units accept data from primary storage to provide users with information or to record the data on a secondary storage device. Some devices are used for both the input and output functions.
The data with which these devices work may or may not be in a form that humans can understand. For example the data that a data entry operator keys into the memory of a computer by typing on a keyboard are readable by humans. However, the data that tell a computer about the performance of an automobile engine are not in a form that humans can read. They are electrical signals from an analog sensor. Similarly, output may be on a printed page, which humans can read easily, or upon some other medium where the data are not visible, such as on magnetic tape or disk.
As we know, all of the data flow from input to final output is managed by the control unit in the CPU. Regardless of the nature of the I/O devices, special processors called I/O interfaces are required to convert the input data to the internal codes used by the computer and to convert internal codes to a format which is usable by the output device.
