How computers work:
The operating system - When a computer is turned
on it searches for instructions in its memory. These instructions tell the
computer how to start up. Usually, one of the first sets of these instructions
is a special program called the operating system, which is the software that makes
the computer work. It prompts the user (or other machines) for input and
commands, reports the results of these commands and other operations, stores
and manages data, and controls the sequence of the software and hardware
actions. When the user requests that a program run, the operating system loads
the program in the computer’s memory and runs the program. Popular operating
systems, such as Microsoft Windows and the Macintosh system (Mac OS), have
graphical user interfaces (GUIs)—that use tiny pictures, or icons, to represent
various files and commands. To access these files or commands, the user clicks
the mouse on the icon or presses a combination of keys on the keyboard. Some
operating systems allow the user to carry out these tasks via voice, touch, or
other input methods.
The computer memory-To process information
electronically, data are stored in a computer in the form of binary digits, or
bits, each having two possible representations (0 or 1). If a second bit is
added to a single bit of information, the number of representations is doubled,
resulting in four possible combinations: 00, 01, 10, or 11. A third bit added
to this two-bit representation again doubles the number of combinations,
resulting in eight possibilities: 000, 001, 010, 011, 100, 101, 110, or 111.
Each time a bit is added, the number of possible patterns is doubled. Eight
bits is called a byte; a byte has 256 possible combinations of 0s and 1s
A byte is a useful quantity
in which to store information because it provides enough possible patterns to
represent the entire alphabet, in lower and upper cases, as well as numeric
digits, punctuation marks, and several character-sized graphics symbols,
including non-English characters such as p. A byte also can be interpreted as
a pattern that represents a number between 0 and 255. A kilobyte—1,024
bytes—can store about 1,000 characters; a megabyte can store about 1 million
characters; a gigabyte can store about 1 billion characters; and a terabyte can
store about 1 trillion characters. Computer programmers usually decide how a
given byte should be interpreted—that is, as a single character, a character
within a string of text, a single number, or part of a larger number. Numbers
can represent anything from chemical bonds to dollar figures to colors to
sounds.
The physical memory of
a computer is either random access memory (RAM), which can be read or changed
by the user or computer, or read-only memory (ROM), which can be read by the
computer but not altered in any way. One way to store memory is within the
circuitry of the computer, usually in tiny computer chips that hold millions of
bytes of information. The memory within these computer chips is RAM. Memory
also can be stored outside the circuitry of the computer on external storage
devices, such as magnetic floppy disks, which can store about 2 megabytes of
information; hard drives, which can store gigabytes of information; compact
discs (CDs), which can store up to 680 megabytes of information; and digital
video discs (DVDs), which can store 8.5 gigabytes of information. A single CD
can store nearly as much information as several hundred floppy disks, and some
DVDs can hold more than 12 times as much data as a CD.
Output devices- Once the CPU has executed
the program instruction, the program may request that the information be
communicated to an output device, such as a video display monitor or a flat
liquid crystal display. Other output devices are printers, overhead projectors,
videocassette recorders (VCRs), and speakers.
Networks - Computers can communicate
with other computers through a series of connections and associated hardware
called a network. The advantage of a network is that data can be exchanged
rapidly, and software and hardware resources, such as hard-disk space or
printers, can be shared. Networks also allow remote use of a computer by a user
who cannot physically access the computer.One type of network, a local area network (LAN), consists of several PCs or workstations connected to a special computer called a server, often within the same building or office complex. The server stores and manages programs and data. A server often contains all of a networked group’s data and enables LAN workstations or PCs to be set up without large storage capabilities. In this scenario, each PC may have “local” memory (for example, a hard drive) specific to itself, but the bulk of storage resides on the server. This reduces the cost of the workstation or PC because less expensive computers can be purchased, and it simplifies the maintenance of software because the software resides only on the server rather than on each individual workstation or PC.
Mainframe computers and supercomputers commonly are networked. They may be connected to PCs, workstations, or terminals that have no computational abilities of their own. These “dumb” terminals are used only to enter data into, or receive output from, the central computer.
Wide area networks (WANs) are networks that span large geographical areas. Computers can connect to these networks to use facilities in another city or country. For example, a person in Los Angeles can browse through the computerized archives of the Library of Congress in Washington, D.C. The largest WAN is the Internet, a global consortium of networks linked by common communication programs and protocols (a set of established standards that enable computers to communicate with each other). The Internet is a mammoth resource of data, programs, and utilities. American computer scientist Vinton Cerf was largely responsible for creating the Internet in 1973 as part of the United States Department of Defense Advanced Research Projects Agency (DARPA). In 1984 the development of Internet technology was turned over to private, government, and scientific agencies. The World Wide Web, developed in the 1980s by British physicist Timothy Berners-Lee, is a system of information resources accessed primarily through the Internet. Users can obtain a variety of information in the form of text, graphics, sounds, or video. These data are extensively cross-indexed, enabling users to browse (transfer their attention from one information site to another) via buttons, highlighted text, or sophisticated searching software known as search engines.
-a system used to link
two or more computers. Network users are able to share files, printers, and
other resources; send electronic messages; and run programs on other computers.
Network software consists of computer programs that establish protocols, or rules, for computers to talk to one another. These protocols are carried out by sending and receiving formatted instructions of data called packets. Protocols make logical connections between network applications, direct the movement of packets through the physical network, and minimize the possibility of collisions between packets sent at the same time.
Network hardware is made up of the physical components that connect computers. Two important components are the transmission media that carry the computer's signals, typically on wires or fiber-optic cables, and the network adapter, which accesses the physical media that link computers, receives packets from network software, and transmits instructions and requests to other computers. Transmitted information is in the form of binary digits, or bits (1s and 0s), which the computer's electronic circuitry can process.
The usefulness and capabilities of personal computers can be greatly enhanced by connection to the Internet and World Wide Web, as well as to smaller networks that link to local computers or databases. Personal computers can also be used to access content stored on compact discs (CDs) or digital versatile discs (DVDs), and to transfer files to personal media devices and video players.
Personal computers are sometimes called microcomputers or micros. Powerful PCs designed for professional or technical use are known as work stations. Other names that reflect different roles for PCs include home computers and small-business computers. The PC is generally larger and more powerful than handheld computers, including personal digital assistants (PDAs) and gaming devices.
Supercomputer, computer designed to perform calculations
as fast as current technology allows and used to solve extremely complex
problems. Supercomputers are used to design automobiles, aircraft, and
spacecraft; to forecast the weather and global climate; to design new drugs and
chemical compounds; and to make calculations that help scientists understand
the properties of particles that make up atoms as well as the behavior and
evolution of stars and galaxies. Supercomputers are also used extensively by
the military for weapons and defense systems research, and for encrypting and
decoding sensitive intelligence information.
Supercomputer
Internet- computer-based global
information system. The Internet is composed of many interconnected computer
networks. Each network may link tens, hundreds, or even thousands of computers,
enabling them to share information and processing power. The Internet has made
it possible for people all over the world to communicate with one another
effectively and inexpensively. Unlike traditional broadcasting media, such as
radio and television, the Internet does not have a centralized distribution
system. Instead, an individual who has Internet access can communicate directly
with anyone else on the Internet, post information for general consumption,
retrieve information, use distant applications and services, or buy and sell
products.