Information Systems Theory

Chapter 4: Input and Output



This chapter discusses various input and output devices. The objectives important to this chapter are:

  1. Understanding four types of input
  2. Understanding the features of keyboards
  3. Understanding mice and other pointing devices
  4. Understanding output, including printed output and display output



Four bullets on page 4.2 summarize four kinds of input:

  • data - raw facts and numbers
  • programs - instructions for a computer
  • commands - often, the signal to begin, end, or modify the execution of a program
  • user responses - information a program may need to begin or complete a task

Keyboards are the most common devices used to give input to a computer. The alphabetic keys are often laid out like a typewriter. Additional keys are often found on a computer keyboard:

  • numeric keypad - a grid of keys resembling those on many calculators, making numeric entry easier.
  • cursor control keys - used to move or position the cursor; keys such as arrows (left, right, up, and down), line movement (HOME and END), and page movement (Page Up and Page Down)
  • lock keys - three keys to set default behaviors:
    • Num Lock - When turned on, this assigns the numeric keypad to act like number keys. When turned off, the numeric keypad acts like arrow keys. Which ever state is in effect, holding a shift key down makes the key act the other way.
    • Caps Lock - When turned on, this locks the alphabetic keys in Capital Letter mode. When turned off, the alphabetic keys are locked in Lower Case mode. Again, whichever state is in effect, pressing a shift key makes the key act the other way.
    • Scroll Lock - When turned on, this is supposed to lock the cursor in one position on the screen and allow the user to move the screen instead of the cursor. I have not used this feature in years. While experimenting for these notes, I could not tell that it had any effect at all in any software I had handy.
  • function keys - these are "extra" keys that are usually assigned different specific functions in different programs. Large applications invariably use the keys, they just do different things in different programs.

Pointing devices come in various types:

  • mouse - first choice for most users, it may have one or more buttons
  • trackball - often integrated into laptop keyboards, sometimes used by people with limited arm movement
  • touchpad - also found on many laptops, sometimes under the name glidepoint
  • pointing stick - I have never heard this generic term. This is actually a small button mounted on a stress gauge, which works as though it were a real joystick. On an IBM ThinkPad, it is called an accupoint.
  • joystick - the main use of joysticks is in games, usually flight simulation and combat games
  • pen input - used in credit card applications, signature collection, and on several types of personal assistant devices
  • touch screen - often used in kiosk devices, such as informational terminals in malls and airports
  • light pen - used to create and change drawings on a screen
  • digitizer - used to scan or trace an existing drawing into a CAD program
  • graphics tablet - used for fine control, and to issue commands to a CAD program

The next topic is Source Data Automation, which means turning a source document into an electronic document without some of the manual labor. Scanners, both handheld and page scanners (also called flatbed scanners) are shown capturing pictures and text to be stored in electronic documents.

Three varieties of Optical Recognition are discussed:

  • Optical Codes - such as scanning bar codes and price codes
  • Optical Marks Recognition - such as scanning answer sheets for quizzes and surveys
  • Optical Character Recognition - such as scanning a printed document to create an electronic copy

Magnetic Ink Character Recognition (MICR) is a technique that is used mainly by banks and credit unions to scan information printed on checks. The check typically has the bank number and account number printed on it in magnetic ink when the user receives the check. The amount a check is written for is printed on it later.

Terminals are usually divided into two types. Dumb terminals do no processing themselves; they only serve to connect to a real computer elsewhere. Smart terminals connect to another computer, but they are capable of processing some instructions themselves. An ATM (Automatic Teller Machine) is given as an example of a smart terminal. It is capable of processing a simple request for a user (like a twenty dollar withdrawal) even if it can't contact the bank's mainframe at the moment.

There are many types of output. The first types discussed on page 4.23 are types of reports:

  • internal reports - these are distributed within an organization
  • external reports - these are given to people outside the organization that produces the reports
  • detail reports - typically, there will be a line in the report for every item in a list, such as a line for every item in an inventory database
  • summary reports - these may summarize information from detail reports, such as reporting only the total number of items in each warehouse, instead of listing each item
  • exception reports - these report only unusual items, such as a list of broken items in a warehouse, instead of all items

Display output is associated with several terms:

  • CRT - a Cathode Ray Tube, or sometimes just tube, is another name for a computer monitor
  • screen - this word may be used to mean the monitor itself, or the current layout of information being shown on a monitor
  • monochrome - a monitor that displays only one color (on a black background) is a monochrome monitor. They are usually green or amber.
  • gray scale - this is a method of displaying pictures on a monochrome monitor using different brightnesses and intensities of the single color to simulate more color depth. An example is a black and white television, which uses a lot of shades of gray.
  • liquid crystal display - a flat panel, often found as a display screen in a laptop computer. Two types are common: passive matrix, which is cheaper and consumes less power, and active matrix, which is brighter (as well as more expensive).
  • pixel - a pixel is another contraction, standing for "picture element". It is one of the "dots" that a monitor's picture is made of.
  • resolution - this is the density of pixels that a monitor can display. Often, monitors can display several densities: VGA resolution is 640 by 480 pixels, while SVGA resolutions include 800 by 600 and 1024 by 768 pixels.
  • dot pitch - this is the distance from the center of one pixel to the center of the nearest pixel on a monitor. Smaller numbers are better. A typical acceptable value for dot pitch is .28 millimeters. .15 would be excellent, .39 would be very grainy.

Printers come in several types:

  • impact printers - something has to hit something to make the output. A dot matrix printer has a series of pins that hit a ribbon to leave a mark on paper. A band printer has hammers that hit a metal band which is embossed with characters, and it hits a ribbon, leaving a mark on paper.
  • ink jet printers - commonly used in homes and offices, these printers spray dots of ink onto paper
  • laser printers - this technology is similar to a photocopier; color laser printers are currently expensive to use and own
  • thermal printers - these produce high quality output by using special dye-impregnated transfer sheets to create glossy color images on output paper
  • plotters - most often used for drafting output, such as blueprints and schematic drawings; able to print to large sheets of paper used by builders and architects

Projectors currently come in two types:

  • projection panel - fits on a standard overhead projector, a computer sends and image to the panel, the projector shines a light through the translucent panel, and an image is projected on a wall or screen
  • LCD projector - brighter than overheads, this device resembles a slide projector. A computer attaches to the device, which uses its own light to project an image.

Microfilm output is often used when keeping records, such as legal records that do not need to be edited, only stored.

Facsimile (FAX) machines come in several varieties. A fax/modem is used to send an image directly from a program to a fax receiver at another site, giving the user much cleaner output than is possible by printing, scanning, sending and receiving (as is done in a traditional fax format).