2. The Information-Processing Machine
Like the Analytical Engine, the computer is a machine that changes
information from one form to another. All computers take in
information (input) and give out information (output).
The computer’s flexibility isn’t hidden in hardware—the physical
parts of the computer system. The secret is software, or programs
—the instructions that tell the hardware what to do to transform
the input data (information in a form that it can read) into the
necessary output.
Evolution and Acceleration
Computer hardware evolved rapidly, with new technologies replacing
old every few years. People sometimes refer to four generations of
computers based on the vacuum tube, the transistor, the integrated
circuit, and the microprocessor. Each of these new technologies
resulted in computer systems that were more reliable, smaller,
faster, more efficient, and cheaper.
Moore’s Law in 1965 predicted that the power of a silicon chip of
the same size would double about every 18 months; this prediction
has been remarkably accurate ever since.
3. The Microcomputer Revolution
A microprocessor contains the critical components of a computer on a
silicon chip. Thanks to the microprocessor, the microcomputer
revolution began in the mid-1970s with the introduction of low-cost,
typewriter-sized computers as powerful as many of the room-sized
computers that had come before.
Personal computers, or PCs, as microcomputers have come to be
known, are now everyday tools in offices, factories, homes, and
schools.
Mainframes and Supercomputers
Before the microcomputer revolution, most information processing
was done on mainframe computers—room-sized machines with
price tags that matched their size. Today, large organizations still use
mainframes for big computing jobs.
Travel agents and bank tellers communicate with a mainframe using
a computer terminal—a combination keyboard and screen that
transfers information to and from the computer. Mainframe
computers are capable of communicating with several users
simultaneously through a technique called timesharing.
4. Workstations and PCs
Servers are computers especially designed to provide software and
other resources to other computers over a network.
A workstation is a high-end desktop computer with the
computing power of a minicomputer at a fraction of the cost.
Workstations are widely used by scientists, engineers, Wall Street
analysts, animators, and others whose work involves intensive
computation. Personal computers are less powerful and less
expensive than workstations, but the line between the two
categories is growing blurry.
5. Portable Computers
Today, one of the fastest growing segments of the PC market
involves machines that aren’t tied to the desktop—portable
computers. Portability is a relative term.
Flat-screen, battery-powered laptop computers are light enough to
rest on your lap while you work or carry like a small briefcase when
closed.
Embedded Computers and Special-Purpose Computers
Not all computers are general-purpose machines. Many are special-
purpose (dedicated) computers that perform specific tasks,
ranging from controlling the temperature and humidity in a high-
rise office building to monitoring your heart rate while you work out.
Embedded computers enhance all kinds of consumer goods:
wristwatches, game machines, stereos, videocassette recorders
(VCRs), ovens, and even automobiles. Embedded computers are also
widely used in industry, the military, and science for controlling a
variety of hardware devices, including robots.
When a program is immortalized on a silicon chip it becomes
firmware—a hybrid of hardware and software.
6. COMPUTER CONNECTIONS
THE INTERNET REVOLUTION
While the world was still reeling from the impact of the
microcomputer revolution, another information technology
revolution was quietly building up steam: a network revolution.
If current trends continue, we’ll look back on the 1990s as the
end of the personal computing era and the beginning of the
interpersonal computing era.
The Emergence of Networks
The first computers were large, expensive, self-contained
machines that could process only one job at a time. The
invention of timesharing in the 1960s allowed multiple users to
connect to a single mainframe computer through individual
terminals. When personal computers started replacing
terminals, they were often linked together in local area
networks so they could share scarce, expensive resources.
7. The Internet Explosion
A few visionary computer scientists and engineers, with financial
backing from the U.S. government, built an experimental network
called ARPANET in 1969. This groundbreaking network would
become the Internet—the global collection of networks that is
radically transforming the way the world uses computers.
Electronic mail (e-mail) made it possible for even casual computer
users to send messages.
In its early years the Internet was the domain of researchers,
academics, and government officials. In the 1990s Internet
software took giant leaps forward in usability. The biggest changes
came with the development of the World Wide Web, a vast tract
of the Internet with a multimedia landscape incorporating
pictures, sounds, animation, and even video.
Web sites designed as first-stop gateways for Internet surfers are
called portals. These are often associated with search engines.
8. THE INTERNET CULTURE
Today, all kinds of people are signing onto the Internet in record
numbers. They use it to communicate with each other, do research,
download music, shop, study, browse, and publish their own work.
Many companies now have intranets – private organizational
networks based on Internet technology. Intranets allow people to
transmit, share, and store information within an enterprise. Several
companies are marketing stripped-down computers designed to
function mainly as network terminals, often called network
computers or information appliances. These allow people to
connect to the Internet without needing a full-blown personal
computer
9. Explanations: Clarifying Technology
Applications
Many people define computer literacy as the ability to use
computers. Application programs, also known simply as
applications, are the software tools that allow a computer to be
used for specific purposes:
Word processing and desktop publishing: Word processing skill is
critical for anyone who communicates in writing. It’s by far the
application used most by students. Desktop publishing uses the
personal computer to transform written words into polished,
visually exciting publications.
Spreadsheets and other number-crunching applications: In
business the electronic spreadsheet is the personal computer
application that pays the rent, or at least calculates it.
Databases for information storage and retrieval: If word
processors and spreadsheets are the most popular PC
applications, databases reign supreme in the world of
mainframes.
10. Databases for information storage and retrieval: If word
processors and spreadsheets are the most popular PC
applications, databases reign supreme in the world of
mainframes.
• Computer graphics: Computers are able to produce all kinds of
graphics, from the charts and graphs produced by spreadsheets
to realistic 3-D animation.
• Multimedia and hypermedia: Multimedia tools for PCs make it
possible to combine audio and video with traditional text and
graphics, adding new dimensions to computer communication.
Hypermedia tools focus on the interactive capabilities of
computers, allowing users to explore a variety of paths through
information sources.
11. • Telecommunication and networking: Every day more
computers are connected — networked — so they can
send information back and forth; we’re entering an era
when networking is the norm. Many experts believe that
telecommunication—long-distance communication—will
be
the single most important function of computers in the
not-too-distant future.
• Artificial intelligence: Artificial intelligence is the
branch of computer science that explores using
computers in tasks that require intelligence,
imagination, and insight—tasks that have traditionally
been performed by people rather than machines.
• General problem solving: People use computers to solve
problems. Programming languages aren’t applications;
they’re tools that allow you to build and customize
12. Implications: Social and Ethical Issues
The immediate potential risks of the computer revolution
are:
The threat to personal privacy posed by large databases
The hazards of high-tech crime and the difficulty of
keeping data secure
The difficulty of defining and protecting intellectual
property
The risks of failure of computer systems
The threat of automation and the dehumanisation of
work
The abuse of information as a tool of political and
economic power
The dangers of dependence on complex technology
13. The longer-term potential risks of the computer
revolution include:
The death of privacy
The blurring of reality
The evolution of intelligence
16. The four basic hardware components of every computer system
are described below.
1. Input devices accept input from the outside world. The most
common input device is the keyboard. Other input devices include
pointing devices like a mouse and joysticks.
2. Output devices send information to the outside world. Most
computers use a TV-like video monitor as their main output
device and some kind of printer for producing paper printouts.
3. A processor, or central processing unit (CPU), processes
information, performing all the necessary arithmetic calculations
and making basic decisions based on information values.
4. Storage devices and memory are used to store information.
The most common storage devices are disk drives and tape drives.
Different types of memory are used for different long-term and
short-term storage tasks.
17. Bits, Bytes, and Buzzwords
Byte: a grouping of 8 bits.
K (kilobyte) (someatimes called KB): about 1000 bytes
of information.
MB (megabyte) (sometimes called meg):
approximately 1000 K, or 1 million bytes.
GB (gigabyte) (sometimes called gig): approximately
1000 megabytes.
TB (terabyte): approximately 1 million megabytes.
18. THE COMPUTERS CORE : THE CPU AND MEMORY
The CPU : The Real Computer
A modern CPU is an extraordinarily complex
collection of electronic circuits When all of those
circuits are built into a single silicon chip, as they
are in most computers today, that chip is referred to
as a microprocessor. In a typical desktop computer,
the CPU is housed along with other chips and
electronic components on a circuit board.
Compatibility. Not all software is compatible with
every CPU; that is, software written for one
processor may not work with another.
19. Speed. A computer’s speed is determined in part by
the speed of its internal clock—the timing device that
produces electrical pulses to synchronize the
computer’s operations. Computers are often described
in terms of their clock speeds, measured in units
called megahertz. Speed is also determined by the
architecture of the processor—the design that
determines how individual components of the CPU are
put together on the chip.
Parallel processing puts more than one processor in
a computer.
20. The Computer’s Memory
RAM (random access memory) is the most common type of
primary storage, or computer memory. RAM chips contain
circuits that can be used to store program instructions and
data temporarily. You can store a piece of information in any
RAM location—you can pick one at random—and the
computer can, if so instructed, quickly retrieve it.
RAM is called volatile memory because information stored
there is not held permanently.
The computer also has nonvolatile memory called ROM
(read-only memory) because the computer can only read
information from it; it can never write any new information
on it. ROM isn’t always hidden away on chips inside the
computer’s chassis. Many home video game machines and
home computers use removable ROM cartridges as
permanent storage devices for games and other programs.
21. Buses, Ports, and Peripherals
Information travels between a computer’s components
through groups of wires called buses. Buses typically
have 8, 16, or 32 wires; a bus with 16 wires is called a
16-bit bus because it can transmit 16 bits of
information at once—twice as many as an 8-bit bus.
Some buses connect to expansion slots inside the
computer’s housing. Users can customize their
computers by inserting special-purpose circuit boards
(usually called cards or just boards) into these slots.
22. Reading Tools
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.
• In many stores bar-code readers are attached to
point-of-sale (POS) terminals. These terminals
send information scanned by the wand to a
mainframe computer.
23. Digitizing the Real World
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.
24. STORAGE DEVICES: INPUT MEETS OUTPUT
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. 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.
25. 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.
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.
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.
There are several choices of removable media to fill the gap between
low-capacity, slow diskettes and nonremovable, fast hard drives:
26. 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—read-only memory) drives are optical
drives capable of reading CD-ROMs—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. CD-RW
(compact disc rewritable) drives can write, erase, and rewrite CDs.
DVD-ROMs (digital versatile disk-read-only memory) will
probably replace CD-ROMs for multimedia applications because of
their enormous capacity.
27. Solid-State Storage Devices
Flash memory is a type of erasable memory chip that
can serve as a reliable, low-energy, quiet, compact
alternative to disk storage. Most experts believe that
solid state storage technology like flash memory will
eventually replace disk and tape storage.
