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How Computers Work: Input and Output
The central processing unit is the unseen part of a computer system, and users are only dimly aware of it. But users are very much aware of the input and output associated with the computer. They submit input data to the computer to get processed information, the output.
Sometimes the output is an instant reaction to the input. Consider these examples:
- Zebra-striped bar codes on supermarket items provide input that permits instant retrieval of outputs - price and item name - right at the checkout counter.
- A bank teller queries the computer through the small terminal at the window by giving a customer's account number as input. The same screen immediately provides the customer's account balance as output.
- A forklift operator speaks directly to a computer through a microphone. Words like left, right, and lift are the actual input data. The output is the computer's instant response, which causes the forklift to operate as requested.
- A medical student studies the human body on a computer screen, inputting changes to the program to show a close-up of the leg and then to remove layers of tissue to reveal the muscles and bone underneath. The screen outputs the changes, allowing the student (without donning a mask, sanitary gloves, or operating gown) to simulate surgery on the computer.
- A sales representative uses an instrument that looks like a pen to enter an order on a special pad. The handwritten characters are displayed as "typed" text and are stored in the pad, which is actually a small computer.
Input and output may sometimes be separated by time or distance or both. Here are some examples:
- Factory workers input data by punching in on a time clock as they go from task to task. The time clock is connected to a computer. The outputs are their weekly paychecks and reports for management that summarize hours per project on a quarterly basis.
- A college student writes checks. The data on the checks is used as input to the bank computer, which eventually processes the data to prepare a bank statement once a month.
- Charge-card transactions in a retail store provide input data that is processed monthly to produce customer bills.
- Water-sample data is collected at lake and river sites, keyed in at the environmental agency office, and used to produce reports that show patterns of water quality.
The examples in this section show the diversity of computer applications, but in all cases the process is the same: input-processing-output. We have already had an introduction to processing. Now, in this chapter we will examine input and output methods in detail.
Input: Getting Data from the User to the Computer
Some input data can go directly to the computer for processing. Input in this category includes bar codes, speech that enters the computer through a microphone, and data entered by means of a device that converts motions to on-screen action. Some input data, however, goes through a good deal of intermediate handling, such as when it is copied from a source document and translated to a medium that a machine can read, such as a magnetic disk. In either case the task is to gather data to be processed by the computer ‹sometimes called raw data and convert it into some form the computer can understand.Keyboard
A keyboard is usually part of a personal computer or part of a terminal that is connected to a computer somewhere else. Not all keyboards are traditional, however. A fast-food franchise like McDonald's, for example, uses keyboards whose keys represent items such as large fries or a Big Mac. Even less traditional in the United States are keyboards that are used to enter Chinese characters.
Mouse
A mouse is an input device with a ball on its underside that is rolled on a flat surface, usually the desk on which the computer sits. The rolling movement causes a corresponding movement on the screen. Moving the mouse allows you to reposition the pointer, or cursor, an indicator on the screen that shows where the next interaction with the computer can take place. The cursor can also be moved by pressing various keyboard keys. You can communicate commands to the computer by pressing a button on top of the mouse. In particular, a mouse button is often used to click on an icon, a pictorial symbol on a screen; the icon represents a computer activity-a command to the computer-so clicking the icon invokes the command.
Trackball
A variation on the mouse is the trackball. You may have used a trackball to play a video game. The trackball is like an upside-down mouse-you roll the ball directly with your hand. The popularity of the trackball surged with the advent of laptop computers, when traveling users found them- selves without a flat surface on which to roll the traditional mouse.
Source Data Automation: Collecting Data Where It Starts
Efficient data input means reducing the number of intermediate steps required between the origination of data and its processing. This is best accomplished by source data automation ‹the use of special equipment to collect data at the source, as a by-product of the activity that generates the data, and send it directly to the computer. Recall, for example, the supermarket bar code, which can be used to send data about the product directly to the computer. Source data automation eliminates keying, thereby reducing costs and opportunities for human-introduced mistakes. Since data about a transaction is collected when and where the transaction takes place, source data automation also improves the speed of the input operation.
For convenience, we will divide this discussion into the primary areas related to source data automation: magnetic-ink character recognition, optical recognition, data collection devices, and even directly by your own voice, finger, or eye. Let us consider each of these in turn.
Magnetic-Ink Character Recognition
Abbreviated MICR, magnetic-ink character recognition is a method of machine-reading characters made of magnetized particles. The most common example of magnetic characters is the array of numbers across the bottom of your personal check.
Most magnetic-ink characters are preprinted on your check. If you compare a check you wrote that has been cashed and cleared by the bank with those that are still unused in your checkbook, you will note that the amount of the cashed check has been reproduced in magnetic characters in the lower-right corner. These characters were added by a person at the bank by using a MICR inscriber.
