Computer:
Computer
technology and Computer system redirect here. For the company, see Computer
Technology Limited. For other uses, see Computer and Computer system.
A computer is a general
purpose device that can be programmed to carry out a set of arithmetic or logical operations.
Since a sequence of operations can be readily changed, the computer can solve
more than one kind of problem.
Conventionally,
a computer consists of at least one processing element, typically a central
processing unit CPU, and some form of memory. The processing element carries
out arithmetic and logic operations, and a sequencing and control unit can
change the order of operations in response to stored information. Peripheral
devices allow information to be retrieved from an external source, and the
result of operations saved and retrieved.
In World
War II, mechanical analog computers were used for specialized military
applications. During this time the first electronic digital computers were
developed. Originally they were the size of a large room, consuming as much
power as several hundred modern personal computers.
Modern
computers based on integrated circuits are millions to billions of times more
capable than the early machines, and occupy a fraction of the space. Simple
computers are small enough to fit into mobile devices, and mobile computers can
be powered by small batteries. Personal computers in their various forms are
icons of the Information Age and are what most people think of as computers.
However, the embedded computers found in many devices from MP3 players
to fighter aircraft and from toys to industrial robots are the most numerous.
What is a Computer:
A computer is a
programmable machine. The two principal characteristics of a computer are it
responds to a specific set of instructions in a well-defined manner and it can execute
a prerecorded list of instructions a program.
Computer is an
electronic device that is designed to work with information. The term computer
id derived from the Latin term Compuware, this means to calculate. Computer can
not do anything without a program. It represents the decimal numbers through a
string of binary digits. The word computer usually refers to the center
processor unit plus internal memory.
Computer
is an advanced electronic device that takes raw data as input from the user and
processes these data under the control of set of instructions and gives the
result and saves output for the future use. It can process both numerical and
non- numerical arithmetic and logical calculation. The basic components of a
modern digital computer are, input device, output device. Central processor. A
typically modern computer uses LSI chips.
Charles Babbage is called the “Grand Father” of the computer. The first
mechanical computer designed by Charles Babbage was called Analytical Engine.
It uses read only memory in the form of punch cards.
Four
Functions about computer are:
Accepts
Data
|
Input
|
Processes
Data
|
Processing
|
Produces
Output
|
Output
|
Stores
Results
|
Storage
|
Input:
Input is the raw information entered into a computer from the
input devices. It is the collection of letters, numbers, images.
Process:
Process is the operation of data as per given instruction. It is
totally internal process of the computer system.
Output:
Output is the processed data given by computer after data processing. Output is also called as Result. We can save these results in the storage devices for the future use.
Computer Definition
A computer is a
device that accepts information and manipulates it for some result based on a program
or sequence of instructions on how the data is to be processed. Complex
computers also include the means for storing data including the program, which
is also a form of data for some necessary duration. A program may be invariable
and built into the computer and called logic circuitry as it is on microprocessor or different programs may
be provided to the computer Today's computers have both kinds of programming.
Most histories of
the modern computer begin with the Analytical Engine envisioned by Charles
Babbage following the mathematical ideas of George Boole, the mathematician who
first stated the principles of logic inherent in today's digital computer.
Babbage's assistant and collaborator, Ada Lovelace, is said to have introduced
the ideas of program loops and subroutines and is sometimes considered the
first programmer. Apart from mechanical calculators, the first really useable
computers began with the vacuum tube, accelerated with the invention of the transistor,
which then became embedded in large numbers in integrated circuits, ultimately
making possible the relatively low-cost personal computer.
Modern computers
inherently follow the ideas of the stored program laid out by John von Neumann
in 1945. Essentially, the program is read by the computer one instruction at a
time, an operation is performed, and the computer then reads in the next
instruction, and so on. Recently, computers and programs have been devised that
allow multiple programs and computers to work on the same problem at the same
time in parallel. With the advent of the Internet and higher bandwidth data
transmission, programs and data that are part of the same overall project can
be distributed over a network and embody the Sun Micro systems slogan, the network is the computer.
First general-purpose computing device
Charles Babbage,
an English mechanical engineer and polymath, originated the concept of a
programmable computer. Considered the father of the computer, he
conceptualized and invented the first mechanical computer in the early 19th
century. After working on his revolutionary difference engine, designed to aid
in navigational calculations, in 1833 he realized that a much more general
design, an Analytical Engine, was possible. The input of programs and data was
to be provided to the machine via punched cards, a method being used at the
time to direct mechanical looms such as the Jacquard loom. For output, the
machine would have a printer, a curve plotter and a bell. The machine would
also be able to punch numbers onto cards to be read in later. The Engine
incorporated an arithmetic logic unit, control flow in the form of conditional
branching and loops, and integrated memory, making it the first design for a
general-purpose computer that could be described in modern terms as Turing-complete.
The machine was about a century ahead of its
time. All the parts for his machine had to be made by hand - this was a major
problem for a device with thousands of parts. Eventually, the project was
dissolved with the decision of the British Government to cease funding.
Babbage's failure to complete the analytical engine can be chiefly attributed
to difficulties not only of politics and financing, but also to his desire to
develop an increasingly sophisticated computer and to move ahead faster than
anyone else could follow. Nevertheless his son, Henry Babbage, completed a
simplified version of the analytical engine's computing unit the mill in
1888. He gave a successful demonstration of its use in computing tables in
1906.
Analog computers
Sir William Thomson's
third tide-predicting machine design,
1879-81
During the
first half of the 20th century, many scientific computing needs were met by
increasingly sophisticated analog computers, which used a direct mechanical or
electrical model of the problem as a basis for computation. However, these were
not programmable and generally lacked the versatility and accuracy of modern
digital computers.
The first
modern analog computer was a
tide-predicting machine, invented by Sir William Thomson in 1872. The
differential analyser, a mechanical analog computer designed to solve
differential equations by integration using wheel-and-disc mechanisms, was
conceptualized in 1876 by James Thomson,
the brother of the more famous Lord
Kelvin.
The art of
mechanical analog computing reached its zenith with the differential analyzer,
built by H. L. Hazen and Vannevar Bush at MIT starting in 1927. This built on the mechanical integrators
of James Thomson and the torque amplifiers invented by H. W. Nieman. A dozen of these devices were built before their
obsolescence became obvious.
The modern computer
The principle of the
modern computer was first described by computer
scientist Alan
Turing, who set out the idea in his
seminal 1936 paper, On Computable Numbers. Turing reformulated Kurt
Godel's 1931 results on the limits of
proof and computation, replacing Gödel's universal arithmetic-based formal
language with the formal and simple hypothetical devices that became known as Turing machines. He proved
that some such machine would be capable of performing any conceivable
mathematical computation if it were represent able as an algorithm. He went on to
prove that there was no solution to the Entscheidungs problem by first
showing that the halting problem for Turing machines is undecidable, in general, it is not possible to decide
algorithmically whether a given Turing machine will ever halt.
He also introduced
the notion of a Universal Machine, with the idea that such a machine could
perform the tasks of any other machine, or in other words, it is provably
capable of computing anything that is computable by executing a program stored
on tape, allowing the machine to be programmable. Von Neumann acknowledged
that the central concept of the modern computer was due to this paper. Turing
machines are to this day a central object of study in theory of computation.
Except for the limitations imposed by their finite memory stores, modern
computers are said to be Turing-complete, which is to say, they have algorithm execution
capability equivalent to a universal Turing
machine.
Electromechanical computers
Early digital
computers were electromechanical - electric switches drove mechanical relays to
perform the calculation. These devices had a low operating speed and were
eventually superseded by much faster all-electric computers, originally using vacuum tubes. The Z2, created by German
engineer Konrad Zuse in 1939, was one of the earliest examples of an electromechanical
relay computer.
In 1941, Zuse
followed his earlier machine up with the Z3, the world's first working electromechanical programmable, fully
automatic digital computer. The Z3 was built with 2000 relays, implementing a
22 bit
word length that operated at a clock frequency of about 5–10 Hz. Program code and data were stored on punched film. It was quite similar
to modern machines in some respects, pioneering numerous advances such as floating point numbers.
Replacement of the hard-to-implement decimal system used in Charles Babbage's earlier design by the simpler binary system meant that
Zuse's machines were easier to build and potentially more reliable, given the
technologies available at that time. The
Z3 was probably a complete Turing machine.
Transistor computers
The bipolar transistor was invented in
1947. From 1955 onwards transistors replaced vacuum
tubes in computer designs, giving rise to
the "second generation" of computers. Compared to vacuum tubes,
transistors have many advantages: they are smaller, and require less power than
vacuum tubes, so give off less heat. Silicon junction transistors were much
more reliable than vacuum tubes and had longer, indefinite, service life.
Transistorized computers could contain tens of thousands of binary logic
circuits in a relatively compact space.
At the University of Manchester,
a team under the leadership of Tom Kilburn designed and built a machine using the newly
developed transistors instead of valves. Their first transistorised
computer and the first in the world, was operational by 1953, and a
second version was completed there in April 1955. However, the machine did make
use of valves to generate its 125 kHz clock waveforms and in the circuitry
to read and write on its magnetic drum
memory, so it was not the first
completely transistorized computer. That distinction goes to the Harwell CADET of 1955,
built by the electronics division of the Atomic
Energy Research Establishment at Harwell.
The defining feature
of modern computers which distinguishes them from all other machines is that
they can be programmed. That is to say that some type of instructions can be given to the computer and it will process
them. Modern computers based on the von
Neumann architecture often have machine
code in the form of an imperative programming
language.
In practical terms,
a computer program may be just a few instructions or extend to many millions of
instructions, as do the programs for word
processors and web browsers for example.
A typical modern computer can execute billions of instructions per second and
rarely makes a mistake over many years of operation. Large computer programs
consisting of several million instructions may take teams of programmers years to
write, and due to the complexity of the task almost certainly contain errors.
Programming language
Programming languages provide
various ways of specifying programs for computers to run. Unlike natural
languages, programming languages are designed to permit no ambiguity and to be
concise. They are purely written languages and are often difficult to read
aloud. They are generally either translated into machine code by a compiler or
an assembler before being run, or translated directly at run time by an
interpreter. Sometimes programs are executed by a hybrid method of the two
techniques.
Low-level languages
Machine
languages and the assembly languages that represent them collectively termed low-level
programming languages tend to be unique to a particular type of
computer. For instance, an ARM architecture computer cannot understand the
machine language of an Intel Pentium or the AMD Athlon 64 computer that might
be in a PC.
Higher-level languages
Though
considerably easier than in machine language, writing long programs in assembly
language is often difficult and is also error prone. Therefore, most practical
programs are written in more abstract high-level programming languages
that are able to express the needs of the programmer more conveniently and
thereby help reduce programmer error. High level languages are usually compiled
into machine language using another computer program called a compiler. High
level languages are less related to the workings of the target computer than
assembly language, and more related to the language and structure of the
problem to be solved by the final program. It is therefore often possible to
use different compilers to translate the same high level language program into
the machine language of many different types of computer. This is part of the
means by which software like video games may be made available for different
computer architectures such as personal computers and various video game
consoles.
Program Design:
Program design of small programs is relatively
simple and involves the analysis of the problem, collection of inputs, using
the programming constructs within languages, devising or using established
procedures and algorithms, providing data for output devices and solutions to
the problem as applicable. As problems become larger and more complex, features
such as subprograms, modules, formal documentation, and new paradigms such as
object-oriented programming are encountered. Large programs involving thousands
of line of code and more require formal software methodologies. The task of
developing large software systems presents a significant intellectual
challenge. Producing software with an acceptably high reliability within a
predictable schedule and budget has historically been difficult; the academic
and professional discipline of software engineering concentrates specifically
on this challenge.
Arithmetic logic unit
The set of
arithmetic operations that a particular ALU supports may be limited to addition
and subtraction, or might include multiplication, division, trigonometry functions
such as sine, cosine, etc., and square
roots. Some can only operate on whole
numbers integers whilst others use floating point to represent real
numbers, albeit with limited precision.
However, any computer that is capable of performing just the simplest
operations can be programmed to break down the more complex operations into
simple steps that it can perform. Therefore, any computer can be programmed to
perform any arithmetic operation—although it will take more time to do so if
its ALU does not directly support the operation. An ALU may also compare
numbers and return boolean truth values true or false depending on whether one is equal to,
greater than or less than the other “is 64 greater than 65?”.
Logic operations
involve Boolean logic: AND, OR, XOR and NOT. These can be useful for creating complicated conditional statements and
processing Boolean logic.
Superscalar computers may contain multiple ALUs, allowing
them to process several instructions simultaneously. Graphics
processors
and computers with SIMD and MIMD
features often contain ALUs that can perform arithmetic on vectors and matrices.
Memory
A computer's memory
can be viewed as a list of cells into which numbers can be placed or read. Each
cell has a numbered “address” and can store a single number. The computer can
be instructed to “put the number 123 into the cell numbered 1357” or to “add
the number that is in cell 1357 to the number that is in cell 2468 and put the
answer into cell 1595.” The information stored in memory may represent
practically anything. Letters, numbers, even computer instructions can be
placed into memory with equal ease. Since the CPU does not differentiate
between different types of information, it is the software's responsibility to
give significance to what the memory sees as nothing but a series of numbers.
In almost all modern
computers, each memory cell is set up to store binary
numbers in groups of eight bits called a byte. Each byte is able to
represent 256 different numbers (2^8 = 256); either from 0 to 255 or −128 to
+127. To store larger numbers, several consecutive bytes may be used typically,
two, four or eight. When negative numbers are required, they are usually stored
in two's complement notation. Other arrangements are possible, but are
usually not seen outside of specialized applications or historical contexts. A
computer can store any kind of information in memory if it can be represented
numerically. Modern computers have billions or even trillions of bytes of
memory.
The CPU contains a
special set of memory cells called registers that can be read and written to much more rapidly
than the main memory area. There are typically between two and one hundred
registers depending on the type of CPU. Registers are used for the most
frequently needed data items to avoid having to access main memory every time
data is needed. As data is constantly being worked on, reducing the need to
access main memory which is often slow compared to the ALU and control units
greatly increases the computer's speed.
Computer main memory
comes in two principal varieties, random-access
memory or RAM and read-only memory or ROM.
RAM can be read and written to anytime the CPU commands it, but ROM is
preloaded with data and software that never changes, therefore the CPU can only
read from it. ROM is typically used to store the computer's initial start-up
instructions. In general, the contents of RAM are erased when the power to the
computer is turned off, but ROM retains its data indefinitely. In a PC, the ROM
contains a specialized program called the BIOS that orchestrates loading the computer's operating system from the
hard disk drive into RAM whenever the computer is turned on or reset. In embedded computers, which
frequently do not have disk drives, all of the required software may be stored
in ROM. Software stored in ROM is often called firmware, because it is notionally more like hardware than
software. Flash memory blurs the distinction between ROM and RAM, as it
retains its data when turned off but is also rewritable. It is typically much
slower than conventional ROM and RAM however, so its use is restricted to
applications where high speed is unnecessary.
In more
sophisticated computers there may be one or more RAM cache memories, which are
slower than registers but faster than main memory. Generally computers with
this sort of cache are designed to move frequently needed data into the cache
automatically, often without the need for any intervention on the programmer's
part.
Main Memory
A PC's main memory
is a fast storage device that is directly accessible by the CPU, and is used to
store the currently executing program and immediately needed data. PCs use semiconductor random access memory RAM
of various kinds such as DRAM, SDRAM or SRAM as their primary storage. Which exact kind depends on
cost performance issues at any particular time. Main memory is much faster than
mass storage devices like hard disks or optical discs, but is usually volatile, meaning it does not retain its contents instructions
or data in the absence of power, and is much more expensive for a given
capacity than is most mass storage. Main memory is generally not suitable for
long-term or archival data storage.
Input/output (I/O)
I/O is the means by
which a computer exchanges information with the outside world. Devices that provide input or output to the computer are called peripherals.
On a typical personal computer, peripherals include input devices like the
keyboard and mouse, and output devices such as the display and printer. Hard
disk drives, floppy disk drives and optical disc drives serve as both input and
output devices. Computer networking is another form of I/O.
I /O devices are
often complex computers in their own right, with their own CPU and memory. A graphics
processing unit might contain fifty or more tiny computers that perform the
calculations necessary to display 3D graphics. Modern desktop computers contain
many smaller computers that assist the main CPU in performing I/O.
Multiprocessing
Some computers are designed to distribute their work across several CPUs in a multiprocessing configuration, a technique once employed only in large and powerful machines such as supercomputers, mainframe computers and servers. Multiprocessor and multi-core multiple CPUs on a single integrated circuit personal and laptop computers are now widely available, and are being increasingly used in lower-end markets as a result.
Supercomputers in
particular often have highly unique architectures that differ significantly
from the basic stored-program architecture and from general purpose computers.
They often feature thousands of CPUs, customized high-speed interconnects, and specialized computing hardware. Such
designs tend to be useful only for specialized tasks due to the large scale of
program organization required to successfully utilize most of the available
resources at once. Supercomputers usually see usage in large-scale simulation, graphics
rendering, and cryptography applications, as well as with other so-called embarrassingly parallel tasks.
Networking and the Internet
Computers have been
used to coordinate information between multiple locations since the 1950s. The
U.S. military's SAGE system was the first large-scale example of such a system,
which led to a number of special-purpose commercial systems such as Sabre.
In the 1970s,
computer engineers at research institutions throughout the United States began
to link their computers together using telecommunications technology. The
effort was funded by ARPA now DARPA and the computer network that resulted was called the
ARPANET. The technologies that made the Arpanet possible spread and evolved.
In time, the network
spread beyond academic and military institutions and became known as the
Internet. The emergence of networking involved a redefinition of the nature and
boundaries of the computer. Computer operating systems and applications were
modified to include the ability to define and access the resources of other
computers on the network, such as peripheral devices, stored information, and
the like, as extensions of the resources of an individual computer. Initially
these facilities were available primarily to people working in high-tech
environments, but in the 1990s the spread of applications like e-mail and the World
Wide
Web, combined with the development of cheap, fast networking
technologies like Ethernet and ADSL saw computer networking become almost
ubiquitous. In fact, the number of computers that are networked is growing
phenomenally. A very large proportion of personal computers regularly connect
to the Internet to communicate and receive information. Wireless networking,
often utilizing mobile phone networks, has meant networking is becoming
increasingly ubiquitous even in mobile computing environments.
A computer
program, or just a program, is a sequence of instructions,
written to perform a specified task with a computer. A computer requires
programs to function, typically executing the program's instructions in a central
processor. The program has an executable form that the computer can use
directly to execute the instructions. The same program in its human-readable source
code form, from which executable programs are derived, enables a programmer to
study and develop its algorithms. A collection of computer programs and related
data is referred to as the software.
Computer source code
is typically written by computer programmers. Source code is
written in a programming language that usually follows one of two main paradigms
imperative or declarative programming. Source code may be converted into an executable
file sometimes called an executable program or a binary by a compiler and later
executed by a central processing unit. Alternatively, computer programs may be
executed with the aid of an interpreter, or may be embedded directly into hardware.
Computer programs
may be ranked along functional lines. System software and application software. Two or more
computer programs may run simultaneously on one computer from the perspective
of the user, this process being known as multitasking.
Computer graphics
Computer graphics are graphics created using computers and the
representation of image data by a computer specifically with help from
specialized graphic hardware and software.
The interaction and
understanding of computers and interpretation of data has been made easier
because of computer graphics. Computer graphic development has had a
significant impact on many types of media and have revolutionized animation, movies
and the video game industry.
History
The phrase Computer
Graphics was coined in 1960 by William
Fetter, a graphic designer for Boeing. The field of computer graphics
developed with the emergence of computer graphics hardware. Early projects like
the Whirlwind and SAGE Projects introduced the CRT as a viable display and
interaction interface and introduced the light pen as an input device. A
programmer for the Whirlwind SAGE system performed a personal experiment in
1954 in which a small program he wrote captured the movement of his finger and
displayed its vector (his traced name) on a display scope. The same individual,
Douglas T. Ross, working at MIT on transforming mathematic statements into
computer generated machine tool vectors in 1959 took the opportunity to create
a display scope image of a Disney cartoon character.
Computer animation
Computer animation
is the art of creating moving images via the use of computers. It is a subfield
of computer graphics and animation. Increasingly it is created by means of 3D
computer graphics, though 2D computer graphics are still widely used for stylistic,
low bandwidth, and faster real-time rendering needs. Sometimes the target of
the animation is the computer itself, but sometimes the target is another medium,
such as film. It is also referred to as CGI Computer-generated imagery or
computer-generated imaging, especially when used in films.
Virtual entities may contain and be
controlled by assorted attributes, such as transform values location,
orientation, and scale stored in an object's transformation matrix. Animation
is the change of an attribute over time. Multiple methods of achieving
animation exist; the rudimentary form is based on the creation and editing of keyframes,
each storing a value at a given time, per attribute to be animated. The 2D/3D
graphics software will change with each keyframes, creating an editable curve
of a value mapped over time, in which results in animation. Other methods of
animation include procedural and expression-based techniques: the former
consolidates related elements of animated entities into sets of attributes,
useful for creating particle effects and crowd simulations, the latter allows
an evaluated result returned from a user-defined logical expression, coupled
with mathematics, to automate animation in a predictable way convenient for
controlling bone behavior beyond what a hierarchy offers in skeletal system set
up.To create the illusion of movement, an image is displayed on the computer screen then quickly replaced by a new image that is similar to the previous image, but shifted slightly. This technique is identical to the illusion of movement in television and motion pictures.
Computer hardware
“Computer hardware” is the
collection of physical elements that constitutes a computer system. Computer
hardware refers to the physical parts or components of a computer such as the monitor, mouse, keyboard, computer data storage, hard drive disk HDD,
system unit graphic cards, sound cards, memory, motherboard and chips, etc. all
of which are physical objects that can be touched. In contrast, software is instructions
that can be stored and run by hardware.
Software is any set
of machine-readable instructions that directs a computer's processor to perform
specific operations. A combination of hardware and software forms a usable
computing system.
Power supply
A power
supply unit converts alternating current electric power to low-voltage DC
power for the internal components of the computer. Laptops are capable of
running from a built-in battery, normally for a period of hours.
Power Supply Unit
The power supply unit
converts general purpose electric current from the mains to direct current for
the other components of the computer. The rated output capacity will be about
40% greater than the calculated system power consumption needs obtained by
adding up all the system components. This protects against overloading the
supply, and guards against performance degradation.
Mother Board
The motherboard is
the main component inside the case. It is a large rectangular board with
integrated circuitry that connects the other parts of the computer including
the CPU,
the RAM,
the disk drives CD, DVD, hard disk, or any others well as any peripherals connected via
the ports or the expansion slots.
Components directly attached to or part of
the motherboard include:- The CPU Central Processing Unit performs most of the calculations which enable a computer to function, and is sometimes referred to as the brain of the computer. It is usually cooled by a heat sink and fan. Most newer CPUs include an on-die Graphics Processing Unit.
- The Chipset, which includes the north bridge, mediates communication between the CPU and the other components of the system, including main memory.
- The “Random-Access Memory” stores the code and data that are being actively accessed by the CPU.
- The “Read-Only Memory” stores the BIOS that runs when the computer is powered on or otherwise begins execution, a process known as Bootstrapping, or "booting" or "booting up". The BIOS Basic Input Output System includes boot firmware and power management firmware. Newer motherboards use Unified Extensible Firmware Interface instead of BIOS.
- Buses connect the CPU to various internal components and to expansion cards for graphics and sound.
The motherboard, also
referred to as system board or main board, is the primary circuit
board within a personal computer. Other major system components plug directly
onto or cable into the motherboard. A motherboard will contain a
microprocessor, the CPU supporting circuitry mostly integrated circuits that
provide the interface between memory and input/output peripheral circuits, main
memory, and facilities for initial setup of the computer immediately after
power on. In many portable and embedded personal computers, the motherboard
houses nearly all of the PC's core components. Often a motherboard will also
contain one or more peripheral buses and physical connectors for expansion
purposes. Sometimes a secondary daughter
board is connected to the motherboard to provide further expandability or
to satisfy space constraints.
Storage Device
Computer data storage, often called storage or
memory, refers to computer components and recording media that retain digital
data. Data storage is a core function and fundamental component of computers.
Input devices allow
the user to enter information into the system, or control its operation. Most
personal computers have a mouse and keyboard, but laptop systems typically use
a touchpad instead of a mouse. Other input devices include webcams, microphones,
joysticks, and image scanners.
Output devices
display information in a human readable form. Such devices could include printers,
speakers, monitors or a Braille embosser.
Keyboard
In computing, a keyboard is an arrangement
of buttons that each correspond to a function, letter, or number. They are the
primary devices of inputting text. In most cases, they contain an array of keys
specifically organized with the corresponding letters, numbers, and functions
printed or engraved on the button. They are generally designed around an
operators language, and many different versions for different languages exist.
In English, the most common layout is the QWERTY layout, which was originally used in typewriters. They have
evolved over time, and have been modified for use in computers with the
addition of function keys, number keys, arrow keys, and OS specific keys.
Often, specific functions can be achieved by pressing multiple keys at once or
in succession, such as inputting characters with accents or opening a task
manager. Programs use keyboard shortcuts very differently and all use different
keyboard shortcuts for different program specific operations, such as refreshing
a web page in a web browser or selecting all text in a word processor.
Mouse
A Mouse on a
computer is a small, sliceable device that users hold and slide around to point
at, click on, and sometimes drag objects on screen in a graphical user
interface using a pointer on screen. Almost all Personal Computers have mice.
It may be plugged into a computer's rear mouse socket, or as a USB device, or,
more recently, may be connected wirelessly via a USB antenna or Bluetooth antenna.
In the past, they had a single button that users could press down on the device
to "click" on whatever the pointer on the screen was hovering over.
Now, however, many Mice have two or three buttons possibly more, a
"right click" function button on the mouse, which performs a
secondary action on a selected object, and a scroll wheel, which users can
rotate using their fingers to "scroll" up or down. The scroll wheel
can also be pressed down, and therefore be used as a third button. Some mouse
wheels may be tilted from side to side to allow sideways scrolling.
Different programs make use of these functions differently, and may scroll
horizontally by default with the scroll wheel, open different menus with
different buttons, among others. These functions may be user defined through
software utilities.
Mice traditionally
detected movement and communicated with the computer with an internal
"mouse ball"; and used optical encoders to detect rotation of the
ball and tell the computer where the mouse has moved. However, these systems
were subject to low durability, accuracy and required internal cleaning. Modern
mice use optical technology to directly trace movement of the surface under the
mouse and are much more accurate, durable and almost maintenance free. They
work on a wider variety of surfaces and can even operate on walls, ceilings or
other non-horizontal surfaces.
Hard disk
Mass storage devices
store programs and data even when the power is off; they do require power to
perform read and write functions during usage. Although flash memory has
dropped in cost, the prevailing form of mass storage in personal computers is
still the hard disk. The disk drives use a sealed head/disk assembly which was
first introduced by IBM's "Winchester" disk system. The use of a
sealed assembly allowed the use of positive air pressure to drive out particles
from the surface of the disk, which improves reliability.
If the mass storage
controller provides for expandability, a PC may also be upgraded by the
addition of extra hard disk or optical disc drives. For example, BD-ROMs, DVD-RWs,
and various optical disc recorders may all be added by the user to certain PCs.
Standard internal storage device connection interfaces are PATA, Serial ATA,
and SCSI.
Mainframe computer
A mainframe
computer is a much larger computer that typically fills a room and may cost
many hundreds or thousands of times as much as a personal computer. They are
designed to perform large numbers of calculations for governments and large
enterprises
Super computer
A supercomputer is superficially similar to a mainframe, but is instead intended for extremely demanding computational tasks. As of November 2013, the fastest supercomputer in the world is the Tianhe, in Guangzhou, China.
Software
Computer software is any kind of computer program, procedure, or
documentation that performs some task on a computer system. The term includes application software such
as word processors which perform productive tasks for users, system software such as operating systems, which
interface with computer hardware to provide the necessary services for application
software, and middleware which controls and co-ordinates distributed systems.
Software
applications for word processing, Internet browsing, Internet
faxing, e-mail and other digital messaging, multimedia playback, computer game play and computer programming are
common. The user of a modern personal computer may have significant knowledge
of the operating environment and application programs, but is not necessarily
interested in programming or even able to write programs for the computer.
Therefore, most software written primarily for personal computers tends to be
designed with simplicity of use, or user-friendliness in
mind. However, the software industry continuously provide a wide range of new products for
use in personal computers, targeted at both the expert and the non-expert user.
Operating system
An operating system OS
manages computer resources and provides programmers with an interface used to access
those resources. An operating system processes system data and user input, and
responds by allocating and managing tasks and internal system resources as a
service to users and programs of the system. An operating system performs basic
tasks such as controlling and allocating memory, prioritizing system requests, controlling input and output devices,
facilitating computer networking and managing files.
Common contemporary
desktop OSs is Microsoft Windows, OS X, Linux, Solaris and FreeBSD. Windows, OS X, and Linux all have server and
personal variants. With the exception of Microsoft Windows, the designs of each
of the aforementioned OSs were inspired by, or directly inherited from, the UNIX operating system. UNIX was developed at Bell Labs beginning in the
late 1960s and spawned the development of numerous free and proprietary
operating systems.
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