Peripherals  

Steve Wozniak, Steve Jobs, and the Garage That Grew Apples

Steve Wozniak, a calculator technician at Hewlett Packard, and Steven Jobs, a free-thinking visionary, formed Apple Computer, Inc. after developing the Apple II, one of the first personal computer systems. The Apple II contained the first disk operating system. Apple had several wildly successful years until IBM's PC eventually dominated the Apple II in the corporate marketplace. Apple's groundbreaking Macintosh established new standards for user friendliness and creativity in personal computers, but it failed to retake the corporate market. Today Macintoshes are most widely used in education, publishing, graphics, and multimedia work. .

 

Input devices allow the computer to receive commands and data from the outside world.

The Omnipresent Keyboard

Typing letters, numbers, and special characters with a computer keyboard is similar to typing on a standard typewriter keyboard. But unlike a typewriter, the computer responds by displaying the typed characters on the screen at the position of the cursor (the current position indicator).

Some keys&endash;cursor (arrow) keys, the Delete or Backspace key, the Enter or Return key, function keys (f-keys), and others&endash;send special commands to the computer.

 

Pointing Devices

Keyboards are used mostly for entering text and numeric data. Pointing devices, such as a mouse or trackball, are used for other traditional keyboard functions, like sending commands and positioning the cursor. Both of these devices are designed to move a pointer around the screen and point to specific characters or objects. The most common type of mouse has a ball on its underside that allows it to roll around on the desktop. The trackball remains stationary on the desk while the user moves the protruding ball to control the pointer on the screen. Both devices have one or more buttons that can be used to send signals to the computer, conveying messages.

As you slide the mouse across your desktop, a pointer echoes your movements on the screen. You can click the mouse&endash;press the button while the mouse is stationary&endash;or drag it&endash;move it while holding the button down.

Examples of other pointing devices:

• The joystick is a favorite as a controller for arcade-style computer games.
• The touch pad or graphics tablet is particularly popular with artists and designers.
• The touch screen can respond when the user points to or touches different screen regions.

Reading Tools

The following reading devices provide the computer with limited ability to "read" directly from paper, converting printed information into bit patterns that can be processed by the computer: 

• Optical-mark readers use reflected light to determine the location of pencil marks on standardized test answer sheets and similar forms.

 

• Bar-code readers use light to read universal product codes (UPCs), inventory codes, and other codes created out of patterns of variable-width bars.

• Magnetic-ink character readers read those odd-shaped numbers printed with magnetic ink on checks.

   

• Wand readers use light to read alphabetic and numeric characters written in a specially designed typeface found on many sales tags and credit card slips. In many stores wand readers are attached to point-of-sale (POS) terminals. These terminals send information scanned by the wand to a mainframe computer.

When wand readers are used to recognize words and numbers at a P0S terminal, the computer is performing optical character recognition (OCR).

Handwritten text analysis is critical in a pen-based computer. This keyboardless machine accepts input from a stylus applied directly to a flat-panel screen.

Many people think the real future of pen-based technology is in personal digital assistants (PDAs), which serve as pocket-sized organizers, notebooks, appointment books, and communication devices for people on the go.

Digitizing the Real World

A computer's ability to recognize handwriting is an example of how it digitizes information&endash;converts it into a digital form that can be stored in the computer's memory.

A variety of input devices have been designed for capturing and digitizing information:

• A scanner is an input device that can make a digital representation of any printed image.
• A digital camera can be used to capture snapshots of the real world as digital images. 
• Audio digitizers contain circuitry to digitize sounds from microphones and other audio devices.
• A video digitizer is a collection of circuits that can capture input from a video source and convert it to a digital signal that can be stored in memory and displayed on computer screens. 
• Sensing devices designed to monitor temperature, humidity, pressure, and other physical quantities provide data used in robotics, environmental climate control, weather forecasting, medical monitoring, biofeedback, scientific research, and hundreds of other applications.

Output devices allow computers to send information to the outside world. The most common output devices are monitor screens and printers.

Screen Output

A video monitor, or video display terminal (VDT), makes it possible for a computer user to see input characters as they're typed, but it also serves as an output device for receiving messages from the computer.

Images on a monitor are composed of tiny dots, called pixels (for picture elements). A square inch of an image on a typical monitor is a grid of about 72 pixels on each side. Such a monitor is said to have a resolution of 72 dots per inch (dpi). The higher the resolution, the closer together the dots.

Most monitors fall into one of two classes: television-style CRT (cathode ray tube) monitors and flat-panel LCD (liquid crystal display) monitors. Both types are available in either color or monochrome models in a variety of sizes. Monochrome monitors display only one color, usually black on white, or green or amber on black.

 

Paper Output

Output displayed on a monitor is immediate, but it's temporary. A printer allows a computer user to produce a hard copy on paper of any information that can be displayed on the computer's screen. Printers come in several varieties, but they all fit into two basic groups:

Impact printers include line printers and dot-matrix printers. The following impact printers form images by physically striking paper, ribbon, and print hammer together, the way a typewriter does: 

• Line printers are used by mainframes to produce massive printouts.
• Dot-matrix printers print text and graphics with equal ease. Instead of printing each character as a solid object, a dot-matrix printer uses pinpoint-sized hammers to create a matrix of tiny dots, some white and some black (or, for color printers, other colors).

Except for applications in which multipart forms must be printed, the following nonimpact printers are gradually replacing impact printers in most offices:

• Laser printers use the same technology as photocopy machines: A laser beam creates patterns of electrical charges on a rotating drum; those charged patterns attract black toner and transfer it to paper as the drum rotates.

 

• Ink-jet printers spray ink directly onto paper.

For certain scientific and engineering applications, a plotter is more appropriate than a printer for producing hard copy. A plotter is, in effect, an automated drawing tool that can produce finely scaled drawings by moving the pen and/or the paper in response to computer commands.

Output You Can Hear

Synthesizers, which are little more than specialized computers designed to generate sounds electronically, can be used to produce music, noise, or anything in between.

 

Controlling Other Machines

Robot arms, telephone switchboards, transportation devices, automated factory equipment, spacecraft, and a host of other machines and systems accept their orders from computers. And of course, computers can send information directly to other computers, bypassing human interaction altogether.

Some computer peripherals are capable of performing both input and output functions. These devices, which include tape and disk drives, serve as secondary storage for the computer. Secondary storage devices allow the computer to record information semipermanently, so it can be read later by the same computer or by another computer.

Magnetic Tape

Tape drives are common storage devices on most mainframe computers and some personal computers. The reason for the widespread use of magnetic tape as a storage medium is because a typical magnetic tape can store massive amounts of information in a small space at a relatively low cost. Most mainframe computers use special tape cartridges, but digital audio tape (DAT) is rapidly becoming the preferred tape for storage on small computers.

Magnetic tape has one clear limitation: Tape is a sequential access medium. Because retrieving information from the middle of a tape is time-consuming, magnetic tape is used today mostly for backup of data and a few other operations that aren't time sensitive.

Magnetic Disks

The magnetic disk is a readily available alternative to tape as a storage medium: A computer's disk drive can rapidly retrieve information from any part of a magnetic disk without regard to the order in which the information was recorded.

Because of their random access capability, disks are far and away the most popular medium for everyday storage needs.

A diskette (or floppy disk) is a small, magnetically sensitive, flexible plastic wafer housed in a plastic case, used to transfer information between machines and for packaging commercial software.

Diskettes are inexpensive, convenient, and reliable, but they lack the storage capacity and drive speed for many large jobs. Most users rely on hard disks as their primary storage devices.

A hard disk is a rigid, magnetically sensitive disk that spins rapidly and continuously inside the computer chassis or in a separate box connected to the computer housing; the user never removes this type of hard disk.

 

Optical Disks

For multimedia applications, optical disks provide a storage alternative to hard disks.

An optical disk drive uses laser beams rather than magnets to read and write bits of information on the disk surface. While they currently aren't as fast as hard disks, optical disks have considerably more room for storing data.

CD-ROM (compact disc&endash;read-only memory) drives are optical drives capable of reading CD-ROMs&endash;data disks that are physically identical to musical compact discs. Because CD-ROMs are read-only devices, they can't be used as secondary storage devices. DVD-ROMs (digital video disk-read-only memory) will probably replace CD-ROMs for multimedia applications because of their enormous capacity.

The complete computer system is a combination of many of the components outlined in the last two chapters; the nature of the system is determined by the hardware components.

Systems Without Boundaries

A computer system can be part of a network that blurs the boundaries between computers, since one computer can, in effect, serve as an input device for another computer, which serves as an output device for the first computer.

The Missing Piece

A complete computer system needs software as well as hardware to function. The next chapter explores the world of software.

Rules of Thumb: Ergonomics and Health

For people who work all day with computers, the side effects include risks to health and safety due to radiation emissions, repetitive-stress injuries like carpal tunnel syndrome, or other computer-related health problems.

Ergonomics (sometimes called human engineering) is the science of designing work environments that allow people and things to interact efficiently and safely.

Ergonomic studies suggest preventive measures you can take to protect your health as you work with computers:

• Choose equipment that's ergonomically designed.
• Create a healthy workspace.
• Rest your eyes.
• Build flexibility into your work environment.
• Listen to your body.

bar-code reader, CD-R drive, CD-ROM, click, CRT (cathode ray tube) monitor

cursor, cursor (arrow) keys, Delete and Backspace keys

digital audio tape (DAT), digital camera, digitize, disk drive, diskette (floppy disk), dot matrix printer

drag, Enter or Return key, ergonomics, function keys (f-keys), graphics tablet, grayscale monitor

hard copy, hard disk, impact printer, inkjet printer, joystick, keyboard, laser printer, LCD (liquid crystal display)

magnetic disk, magnetic-ink character reader, magnetic tape, magneto-optical disks, monitor line printer, monochrome monitor, mouse

nonimpact printer, optical character recognition (OCR), optical disk, optical disk drive, optical-mark reader

pen-based computer, personal digital assistant (PDA), pixel, plotter, point-of-sale (POS) terminal, printer

random access, removable media, repetitive-stress injuries, resolution

scanner, secondary storage, sensing device, sequential access, tape drive, touch pad, touch screen

trackball, track point, video display terminal (VDT), video monitor, wand reader, WORM (write once, read many) drive

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