Caribbean Secondary Education Certificate - Information Technology/Input Devices and Media
Input Devices and Media
An input device is any peripheral (piece of computer hardware equipment) used to provide data and control signals to an information processing system (such as a computer). Input and output devices make up the hardware interface between a computer as a scanner or six degrees of freedom (6DOF) controller.
Many input devices can be classified according to:
- the modality of input (e.g. mechanical motion, audio, visual, etc.)
- whether the input is discrete (e.g. keypresses) or continuous (e.g. a mouse's position, though digitized into a discrete quantity, is fast enough to be considered continuous)
- the number of degrees of freedom involved (e.g. two-dimensional traditional mice, or three-dimensional navigators designed for CAD applications)
Pointing devices, which are input devices used to specify a position in space, can further be classified according to:
- Whether the input is direct or indirect. With direct input, the input space coincides with the display space, i.e. pointing is done in the space where visual feedback or the cursor appears. Touchscreens and light pens involve direct input. Examples involving indirect input include the mouse and trackball.
- Whether the positional information is absolute (e.g. on a touch screen) or relative (e.g. with a mouse that can be lifted and repositioned)
Note that direct input is almost necessarily absolute, but indirect input may be either absolute or relative. For example, digitizing Graphics tablets that do not have an embedded screen involve indirect input, and sense absolute positions and are often run in an absolute input mode, but they may also be setup to simulate a relative input mode where the stylus or puck can be lifted and repositioned.
- Unit Record Equipment
Before the advent of electronic computers, data processing was performed using electromechanical devices called unit record equipment, electric accounting machines (EAM) or tabulating machines. Unit record machines were as ubiquitous in industry and government in the first half of the twentieth century as computers became in the second half. They allowed large volume, sophisticated, data-processing tasks to be accomplished long before modern (electronic) computers were invented. This data processing was accomplished by processing decks of punched cards through various unit record machines in a carefully choreographed progression. This progression, or flow, from machine to machine was often planned and documented with drawings that used standardised symbols for the various machine functions – drawings that today would be called flowcharts. The machines all had high-speed mechanical feeders to process from around one hundred cards per minute, to 2,000 cards per minute, sensing punched holes with either electrical or optical sensors. The operation of many machines was directed by the use of a removable control panel. Initially all machines were constructed using electromechanical counters and relays. Electronic components were introduced on some machines beginning in the late 1940s.
Examples of Earlier Versions
- Punch Cards - The basic unit of data storage was the 80-column punched card. Each punched column represented a single digit, letter or special character. Data values consisted of a field of adjacent columns. An employee number might occupy 5 columns; hourly pay rate, 3 columns; hours actually worked in a given week, 2 columns; department number 3 columns; project charge code 6 columns and so on.
- Keypunching - Original data was usually punched into cards by workers, often women, known as key punch operators. Their work was often checked by a second operator using a verifier machine. Cards were also produced automatically by various unit record machines and later by computer output devices.
- Sorting - A major activity in any unit record shop was sorting decks of punch card into the proper order as determined by information punched in the card. The same deck might be sorted differently depending on the processing step. Sorters, like the IBM 80 series Card Sorters, sorted an input deck into one of 13 output bins depending on which hole was punched in a selected column. The 13th bin was for blanks and rejects. Sorting an input deck into ascending sequence on a multiple column field, such as an employee number, was done by a radix sort.
Data processing tasks typically ran on a daily batch processing cycle. All the data cards punched during the day were sorted and merged with a master deck, which was then tabulated.
- Tabulating - Reports and summary data were generated by accounting or tabulating machines. The sorted deck was fed through the tabulating machine and each card was printed on its own line. Selected fields from each card were added to the value of one of several counters. At some signal, say a card with a special punch indicating it was a master card, a summary line would be produced containing the summed values.
- Card Punching - Card punching machines included:
- Gang punch - these would produce a large number of identically punched cards—for example, for inventory tickets.
- Reproducing punch - these could reproduce a deck of cards in its entirety or they might just reproduce selected fields. A payroll master deck might be reproduced at the end of a pay period with the hours worked and net pay fields blank and ready for the next pay period's data. Computer programmers who created their programs in the form of punch card decks used these to make backups.
- Summary punch - these were attached to tabulating machines and could punch new cards with details and totals from the tabulating machine.
- Mark sense reader - these would detect pencil marks on bubbles printed on the card and punch the corresponding data values into the card.
- Mark sense (Electrographic) cards, developed by Reynold B. Johnson at IBM, had printed ovals that could be marked with a special electrographic pencil. Cards would typically be punched with some initial information, such as the name and location of an inventory item. Information to be added, such as quantity of the item on hand, would be marked in the ovals. Card punches with an option to detect mark sense cards could then punch the corresponding information into the card
- Aperture cards have a cut-out hole on the right side of the punched card. A 35 mm microfilm chip containing a microform image is mounted in the hole. Aperture cards are used for engineering drawings from all engineering disciplines. Information about the drawing, for example the drawing number, is typically punched and printed on the remainder of the card. Aperture cards have some advantages over digital systems for archival purposes.
A keyboard is a human interface device which is represented as a layout of buttons. Each button, or key, can be used to either input a linguistic character to a computer, or to call upon a particular function of the computer. Traditional keyboards use spring-based buttons, though newer variations employ virtual keys, or even projected keyboards. Examples of types of keyboards include:
- Computer keyboard
- Chorded keyboard
- LPFK (Lighted Program Function Keyboard)
A pointing device is any human interface device that allows a user to input spatial data to a computer. In the case of mice and touch screens, this is usually achieved by detecting movement across a physical surface. Analog devices, such as 3D mice, joysticks, or pointing sticks, function by reporting their angle of deflection. Movements of the pointing device are echoed on the screen by movements of the cursor, creating a simple, intuitive way to navigate a computer's graphical user interface.
Imaging and Video Input Devices
Video input devices are used to digitize images or video from the outside world into the computer. The information can be stored in a multitude of formats depending on the user's requirement.
- Image scanner
- Fingerprint scanner
- Barcode reader
- 3D scanner
- Laser rangefinder
- Medical Imaging
- Computed tomography
- Magnetic resonance imaging
- Positron emission tomography
- Medical ultrasonography
Audio Input Devices
In the fashion of video devices, audio devices are used to either capture or create sound. In some cases, an audio output device can be used as an input device, in order to capture produced sound.
- MIDI keyboard or other digital musical instrument