Computer keyboard

A  computer keyboard is a peripheral modeled after the typewriter keyboard. Keyboards
are designed for the input of text and characters, and also to control the operation of the computer.
Physically, computer keyboards are an arrangement of rectangular or near-rectangular buttons, or
"keys". Keyboards typically have characters engraved or printed on the keys; in most cases, each
press of a key corresponds to a single written symbol. However, to produce some symbols requires
pressing and holding several keys simultaneously, or in sequence; other keys do not produce any
symbol, but instead affect the operation of the computer, or the keyboard itself. See input method
editor.

Roughly 50% of all keyboard keys produce letters, numbers or signs (characters). Other
keys can produce actions when pressed, and other actions are available by simultaneously pressing
more than one action key.

Secondary storage

In computer storage,  secondary storage, or  external memory, is computer memory that is
not directly accessible to the central processing unit of a computer, requiring the use of computer's
input/output channels. Secondary storage is used to store data that is not in active use. Secondary
storage is usually slower than  primary storage, or internal memory, but also almost always has
higher storage capacity and is non-volatile, preserving the stored information in an event of power
loss.
Storage devices in this category include:
•  CD, CD-R, CD-RW
•  DVD
•  Flash memory
•  Floppy disk
•  Hard disk
•  Magnetic tape
•  Paper tape
•  Punch card
•  RAM disk

Generations Of Optical Discs

First-generation optical discs

Optical discs were initally used for storing music and software. The Laser disc format stored
analog video, but it fought an uphill battle against VHS.
•  Compact disc (CD)
•  Laser disc
•  Magneto-optical disc

Second-generation optical discs

These discs were invented roughly in the 1990s. Second-generation optical discs were
created to store large amounts of data, including TV-quality digital video.
•  Mini disc
•  Digital Versatile Disc (DVD)
•  Digital Multilayer Disk
•  Digital Video Express
•  Fluorescent Multilayer Disc
•  GD-ROM
•  Phase-change Dual
•  Universal Media Disc

Third-generation optical discs

Major third-generation optical discs are currently in development. They will be optimal for
storing high-definition video and extremely large video games.
•  Blu-ray Disc
•  Enhanced Versatile Disc
•  Forward Versatile Disc
•  Holographic Versatile Disc
•  HD DVD
•  Ultra Density Optical
•  Professional Disc for DATA
•  Versatile Multilayer Disc

Optical disc

In computing, sound reproduction, and video, an  optical disc is flat, circular, usually
polycarbonate disc whereon data is stored. This data is generally accessed when a special material
on the disc (often aluminum) is illuminated with a laser diode.
David Paul Gregg developed an analog optical disk for recording video and patented it in
1961 and 1969 (U.S. patent 3430966). Of special interest is U.S. 4,893,297, first filed in 1968 and
issued in 1990, so that it will be a source of royalty income for  Pioneer’s DVA until 2007. It
encompasses systems such as CD, DVD, and even Blu-ray Disc. Gregg's company, Gauss
Electro physics, was acquired, along with Gregg's patents, by MCA in the early 1960s.
Parallel, and probably inspired by the developments in the U.S., a small group of physicists
started their first optical videodisc experiments at Philips Research in Eindhoven, The Netherlands
in 1969. In 1975, Philips and MCA decided to join forces. In 1978, much too late, the long waited
laser disc was introduced in Atlanta. MCA delivered the discs and Philips the players. It turned out
to be a total technical and commercial failure, and quite soon the Philips/MCA cooperation came to
an end. In Japan and the U.S., Pioneer has been successful with the  videodisc till the advent of
DVD.
Philips and Sony formed a consortium in 1979 to develop a digital audio  disc, which
resulted in the very successful introduction of the compact disc in 1983.
The promotion of standardized optical storage is undertaken by the Optical Storage
Technology Association (OSTA).
The information on an optical disc is stored sequentially on a  continuous spiral track from
the innermost track to the outermost track.

Domestic mains adaptors

A  power supply (or in some cases just a transformer) that is built into the top of a plug is
known as a wall wart, power brick, or just power adapter.

Linear power supply

A simple AC powered linear power supply uses a transformer to convert the voltage from
the wall outlet to a lower voltage. A diode circuit (generally  either a single diode or an array of
diodes called a diode bridge but other configurations are possible)  then rectifies the AC voltage to
pulsating DC. A capacitor smooths out most of the pulsating of the rectified waveform to give a DC
voltage with some ripple. Finally depending on the requirements of the load a linear regulator may
be used to reduce the voltage to the desired output voltage and remove the majority of the
remaining ripple. It may also provide other features such as current limiting.

Switched-mode power supply

In a  switched-mode power supply the incoming power is passed through a transistor and
transformer network that switches on and off thousands to millions of times per second. This means
that a smaller, less expensive, lighter transformer can be used, because the voltage is being made to
alternate faster, and thus a smaller magnetic core can be used.
Switching power supplies can be used as DC to DC converters. In  this application, the
power supply is designed to accept a limited range DC input and then output a different DC voltage.
This is particularly useful in portable devices, as well as  power distribution in large electronic
equipment. A transformer less switching power supply that outputs a voltage higher than its input
voltage is typically called a boost converter. A transformer less switching power supply that outputs
a voltage lower than its input voltage is typically called a  buck converter. These transformer less
switching power supplies use an inductor as the primary circuit element in converting the voltage.
Circuitry is used to pass current through the inductor to store a certain amount of electrical energy
as a magnetic field. The current flow is then stopped, and the magnetic field collapses causing the
stored energy to be released as current again. This is done rapidly (up to millions of times per
second). By carefully metering the amount of energy stored in the inductor, the current released by
the inductor can be regulated thus allowing the output voltage to be tightly regulated. A switching
power supply incorporating a transformer can provide many output voltages simultaneously, and is
typically called a  fly back converter. Switching power supplies are typically very efficient if well
designed, and therefore waste very little power as heat. Because of these efficiencies, they are
typically much smaller and lighter than an equivalently rated linear supply.


Power conversion

The term "power supply" is sometimes restricted to those devices that  convert some other
form of energy into electricity(such as solar power and fuel cells and generators). A more accurate term for devices that convert one form of electric power into another form of electric
power (such as transformers and linear regulators) is power converter.
Uses in aviation
The most exotic power supplies are used in aviation to enable reliable restarting of stalled
engines.
In jet transports, an engine is restarted from the power produced by the 400 Hz, three-phase AC
generators attached to the shafts of the other engine(s). Most of the starting torque generated by the
engine's motor/generator is provided by the current at the peaks of the AC waveform.
If the aircraft electronics used simple rectifying power supplies, they would use current only
from these peaks, since the diodes conduct only during the voltage peaks  where the input voltage is
higher than the output voltage. This could prevent the pilot from restarting an engine in an
emergency.
Therefore, aircraft power supplies take energy evenly from all parts of the AC waveform.
this is done by using a switching power supply technique called "power factor correction" which
creates a balanced current draw over the entire AC waveform.

Computer power supply

A computer power supply typically is designed to convert 120 V or 240 V AC power from
the electrical company to usable power for the internal components of the computer. The most
common computer power supply is built to conform with the ATX form factor. This enables
different power supplies to be interchangeable with different components inside the computer. ATX
power supplies also are designed to turn on and off using a signal from the motherboard (PS-ON
wire), and provide support for modern functions such as the Standby mode of many computers.
Computer power supplies are rated for certain wattages based on their maximum output
power. Typical wattages range from 200 W to 500 W, although some new personal computers with
high energy requirements may draw as much as 1000 W (1 kW).

Most computer power supplies have a large bundle of wires emerging from one end. One
connector attached to the opposite end of some wires goes to the motherboard to provide power.
The PS-ON wire is located in this connector. The connector for the motherboard is typically the
largest of all the connectors. There are also other, smaller connectors, most of which have four
wires: two black, one red, and one yellow. Unlike the standard electrical wire color-coding, each
black wire is a Ground, the red wire is +5 V, and the yellow wire is +12 V.

Inside the computer power supply is a complex arrangement of electrical components,
ranging from diodes to capacitors to transformers. Also, many power supplies have metal heat sinks
and fans to dissipate large amounts of heat produced. It is dangerous to open a power supply while it is connected to an electrical outlet as high voltages may be present even while the unit is switched
off.
In desktop computers, the power supply is a small (PSU) box inside the computer; it is an
important part of the computer because it provides electrical power in a form that is suitable for
every other component inside or attached to the computer in order for it to work. If only a small
voltage is needed, the mains power needs to be transformed to a suitable level in order for the
component to work.
In portable computers there is usually an external power supply that produces low voltage
DC power from a mains electrical supply (typically a standard AC wall outlet). Circuitry inside the
portable computer uses this transformed power to charge the battery as needed, in addition to
providing the various voltages required by the other components of the portable computer.

Power supply

A power supply(sometimes known as a  power supply unitor PSU) is a device or system
that supplies electrical or other types of energy to an output load or group of loads. The term is most
commonly applied to electrical energy supplies.
The complete range of power supplies is very broad, and could be considered to include all
forms of energy conversion from one form into another. Conventionally though, the term is usually
confined to electrical or mechanical energy supplies. Constraints that commonly affect power
supplies are the amount of power they can supply, how long they can supply it for without needing
some kind of refueling or recharging, how stable their output voltage or current is under varying
load conditions, and whether they provide continuous power or pulses.
The voltage regulation of power supplies is done by incorporating circuitry to tightly control
the output voltage and/or current of the power supply to a specific value. The specific value is
closely maintained despite variations in the load presented to the power supply's output, or any
reasonable voltage variation at the power supply's input.

A "wall wart" style variable DC power supply with its cover removed. Simpler AC supplies
have nothing inside the case except the transformer.
This term covers the mains power distribution system together with any other primary or
secondary sources of energy such as:
•  Conversion of one form of electrical power to another desired form and  voltage. This
typically involves converting 120 or 240 volt AC supplied by a utility company (see electricity
generation) to a well-regulated lower voltage DC for electronic devices. For examples, see
switched-mode power supply, linear regulator, rectifier and inverter (electrical).
•  Batteries
•  Chemical fuel cells and other forms of energy storage systems
•  Solar power
•  Generators or alternators (particularly useful in vehicles of  all shapes and sizes, where the
engine has rotational power to spare, or in semi-portable units  containing an internal combustion
engine and a generator) (For large-scale power supplies, see  electricity generation.) Low voltage,
low power DC power supply units are commonly integrated with the devices they supply, such as
computers and household electronics.

History of the expansion card

The first microcomputer to feature a slot-type expansion card  bus was the Altair 8800,
developed 1974-1975. Initially, implementations of this bus were proprietary (such as the Apple II
and Macintosh), but by 1982 manufacturers of Intel 8080/Zilog Z80-based computers running
CP/M had settled around the S-100 standard. IBM introduced the XT bus with the first IBM PC in
1983. XT was replaced with ISA in 1984. IBM's MCA bus, developed for  the PS/2 in 1987, was a
competitor to ISA, but fell out of favor due to the latter's industry-wide acceptance. EISA, the 16-bit
extended version of ISA, was common on PC motherboards until 1997, when Microsoft declared it
as "legacy" subsystem in the PC 97 industry white-paper. VESA Local Bus, an early expansion bus
that was inherently tied to the 80486 CPU, became obsolete (along  with the processor) when Intel
launched the Pentium processor in 1996.
The PCI bus was introduced in 1991 as replacement for ISA. The standard (now at version 2.2) is
still found on PC motherboards to this day. Intel introduced the AGP busin 1997 as a dedicated video acceleration solution. Though termed a bus, AGP supports only a single card at a time. Both
of these technologies are now slated to be replaced by PCI-Express, beginning in 2005. This latest
standard, approved in 2004, implements the logical PCI protocol over serial communication
interface.
Expansion slot standards
•  PCI Express
•  AGP
•  PCI
•  ISA
•  MCA
•  VLB
•  Card Bus/PC card/PCMCIA (for notebook computers)
•  Compact flash (for handheld computers)
Expansion card types
•  Graphics card
•  Sound card
•  Network card
•  TV card
•  Modems
•  Wireless network (such as WiFi) cards.
•  Hard disk/RAID controllers (host adapter)
•  POST cards
•  Physics cards, only recently became commercially available

Expansion card

An  expansion card in computing is a printed circuit board that can be inserted into an
expansion slot of a computer motherboard to add additional functionality  to a computer system.
One edge of the expansion card holds the contacts that fit exactly into the slot. They establish the
electrical contact between the electronics (mostly integrated circuits) on the card and on the
motherboard.
Connectors mounted on the bracket allow the connection of external devices to the card.
Depending on the form factor of the motherboard and case, around one to seven expansion cards
can be added to a computer system. There are also other factors involved in expansion card
capacity. For example, some expansion cards need two slots like  some Nvidia Get Force FX
graphics cards and there is often a space left to aid cooling on some high-end cards.

Technology and history

Today, primary storage is typically random access memory, atype of semiconductor
memory. Over the history of computing hardware, a variety of  technologies have been used for
primary storage. Some early computers used mercury delay lines, in which a series of acoustic
pulses were sent along a tube filled with mercury. When the pulse reached the end of the tube, the
circuitry detected whether the pulse represented a binary 1  or 0 and caused the oscillator at the
beginning of the line to repeat the pulse. Other early computers stored primary memory on rapidly
rotating magnetic drums.
Modern primary storage devices include:
•  Random access memory (RAM) - includes VRAM, WRAM, NVRAM
•  Read-only memory (ROM)

Primary storage

Primary storage, or internal memory, is computer memory that is accessible to the central
processing unit of a computer without the use of computer's input/output channels. Primary storage
is used to store data that is likely to be in active use. Primary storage is typically very fast, in the
case of RAM which is also volatile, losing the stored information in an event of power loss, and
quite expensive. ROM is not volatile, but not suited to storage of large quantities of data because it
is expensive to produce. Typically, ROM must also be completely erased before it can be rewritten,
making large scale use impractical, if not impossible. Therefore, separate  secondary storage, or
external memory, is usually required for long-term persistent storage.

Confusingly, the term primary storage has recently been used in  a few contexts to refer to
online storage (hard disks), which is usually classified as secondary storage.
Primary storage may include several types of storage, such as main storage, cache memory, and
special registers, all of which can be directly accessed by the processor. Primary storage can be
accessed randomly, that is, accessing any location in storage at any moment takes the same amount of time. A particular location in storage is selected by its physical memory address. That address
remains the same, no matter how the particular value stored there changes.

Central processing unit

The central processing unit, or CPU, is the part of the computer that executes software
programs, including the operating system. Nearly all PCs contain a type of CPU known as a
microprocessor. The microprocessor often plugs into the motherboard using one of many different
types of sockets. IBM PC compatible computers use an x86-compatible processor, usually made by
Intel, AMD, VIA Technologies or Trans meta. Apple Macintosh processors were based on the
Power PC (a RISC architecture) but as of 2005, Apple has used x86 compatible processors from
Intel.

A  central processing unit(CPU), or sometimes simply  processor,is the component in a
digital computer that interprets instructions and processes data contained in computer programs.
CPUs provide the fundamental digital computer trait of programm ability, and are one of the
necessary components found in computers of any era, along with primary storage and input/output
facilities. A CPU that is manufactured using integrated circuits is known as a microprocessor. Since
the mid-1970s, single-chip microprocessors have almost totally replaced all other types of CPUs,
and today the term "CPU" is usually applied to some type of microprocessor.
The phrase "central processing unit" is, in general terms, a description of a certain class of
logic machines that can execute complex computer programs. This broad definition can easily be
applied to many early computers that existed long before the term "CPU" ever came into
widespread usage. However, the term itself and its initialism have been in use in the computer
industry at least since the early 1960s (Weik 1961). The form, design and implementation of CPUs
have changed dramatically since the earliest examples, but  their fundamental operation has
remained much the same.
Early CPUs were custom-designed as a part of a larger, usually one-of-a-kind, computer.
However, this costly method of designing custom CPUs for a particular application has largely
given way to the development of inexpensive and standardized classes of processors that are suited
for one or many purposes. This standardization trend generally began in the era of discrete transistor
mainframes and minicomputers and has rapidly accelerated with the popularization of the integrated
circuit (IC). The IC has allowed increasingly complex CPUs to be designed and manufactured in
very small spaces (on the order of millimeters). Both the miniaturization and standardization of
CPUs have increased the presence of these digital devices in modern life far beyond the limited
application of dedicated computing machines. Modern microprocessors appear in everything from
automobiles to cell phones to children's toys.

Motherboard

The motherboard (or mainboard ) is the primary circuit board fora personal microcomputer.
Many other components connect directly or indirectly to the motherboard. Motherboards usually
contain one or more CPUs, supporting circuitry and ICs for CPU operation, main memory, and
facilities for initial setup of the computer immediately after being powered on (often called boot
firmware or a BIOS). 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 with the motherboard to provide further expandability or to satisfy space
constraints.

Display

A computer display(also known as a  computer monitor,  computer screen, or  computer
video display) is a device that can display signals generated by a computer as images on a screen.
There are many types of monitors, but they generally conform to  display standards. Once an
essential component of computer terminals, computer displays have long since become standardized
peripherals in their own right.

Configuration

 

Exploded view of a modern personal computer:
1.  Display
2.  Motherboard
3.  CPU (Microprocessor)
4.  Primary storage (RAM)
5.  Expansion cards
6.  Power supply
7.  Optical disc drive
8.  Secondary storage (HD)
9.  Keyboard
10.  Mouse
Personal computers can be categorized by size and portability:
•  Desktop computers
•  Laptop or notebooks
•  Personal digital assistants (PDAs)
•  Portable computers 
•  Tablet computers
•  Wearable computers

Most personal computers are standardized to the point that purchased software is expected
to run with little or no customization for the particular computer.  Many PCs are also user-upgradable, especially desktop and workstation class computers. Devices such as main memory,
mass storage, even the motherboard and central processing unit maybe easily replaced by an end
user. This upgradeability is, however, not indefinite due to rapid changes in the personal computer
industry. A PC that was considered top-of-the-line five or six years prior may be impractical to
upgrade due to changes in industry standards. Such a computer usually  must be totally replaced
once it is no longer suitable for its purpose. This upgrade and replacement cycle is partially related
to new releases of the primary mass-market operating system, which tends to drive the acquisition
of new hardware and tends to obsolete previously serviceable hardware (see planned obsolescence).
The hardware capabilities of personal computers can sometimes be extended by the addition of
expansion cards connected via an expansion bus. Some standard peripheral buses often used for
adding expansion cards in personal computers as of 2005 are PCI, AGP  (a high-speed PCI bus
dedicated to graphics adapters), and PCI Express. Most personalcomputers as of 2005 have
multiple physical PCI expansion slots. Many also include an AGP bus and expansion slot or a PCI
Express bus and one or more expansion slots, but few PCs contain both buses.

Uses

Personal computers are normally operated by one user at a time to perform such general
purpose tasks as word processing, internet browsing, e-mail and  other digital messaging,
multimedia playback, video game play, computer programming, etc. Other more specific functions
usually performed with the help of a PC include working, teleworking, learning, researching,
printing, online banking, online shopping and dealing online with public sector institutions and
services. 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 nor 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 foruse in personal computers,
targeted at both the expert and the non-expert user.

A history of personal computers

A personal computer (PC) is usually a microcomputer whose price, size, and capabilitiesmake it suitable for personal usage. The term was popularized by IBM marketing

Time share "terminals" to central computers were sometimes used before the advent of the PC.
(A smart terminal — televideo ASCII character mode terminal made around 1982.)
Before their advent in the late 1970s to the early 1980s, the only computers one might have
used if one were privileged were "computer-terminal based" architectures owned by large
institutions. In these, the technology was called "computer time share systems", and used
minicomputers and main frame computers. These central computer systems frequently required
large rooms — roughly, a handball-court-sized room could hold two to three small minicomputers
and its associated peripherals, each housed in cabinets much the size of three refrigerators side by
side (with blinking lights and tape drives). In that era, mainframe computers occupied whole floors;
a big hard disk was a mere 10–20 Megabytes mounted on a cabinet the size of a small chest-type
freezer. Earlier PCs were generally called desktop computers, and the slower Pentium-based
personal computer of the late 1990s could easily outperform the advanced minicomputers of that
era.
Since the terms "personal computer" and "PC" have been introduced to vernacular language,
their meanings and scope have changed somewhat. The first generations of personal
microcomputers were usually sold as kits or merely instructions, and required a somewhat skilled
person to assemble and operate them. These were usually called microcomputers, but personal
computer was also used. Later generations were sometimes interchangeably called by the names "home computer" and "personal computer." By the mid-1980s, "home computer" was becoming a
less common label in favor of "personal computer." These computers were pre-assembled and
required little to no technical knowledge to operate. In today's common usage, personal computer
and PC usually indicate an IBM PC compatible. Because of this association, some manufacturers of
personal computers that are not IBM PCs avoid explicitly using the terms to describe their products.
Mostly, the term PC is used to describe personal computers that use Microsoft Windows operating
systems.


A four-megabyte RAM card measuring about 22 by 15 inches; made for the VAX 8600
minicomputer (circa 1986). Dual in-line package (DIP) Integrated circuits populate nearly the
whole board; the RAM chips are in the majority located in the rectangular areas to the left and right.
One early use of "personal computer" appeared in a 3 November 1962, New York Times article
reporting John W. Mauchly's vision of future computing as detailed at a recent meeting of the
American Institute of Industrial Engineers. Mauchly stated, "There is no reason to suppose the
average boy or girl cannot be master of a personal computer." [1] Some of the first computers that
might be called "personal" were early minicomputers such as the LINC and PDP-8. By today's
standards they were very large (about the size of a refrigerator) and cost prohibitive (typically tens
of thousands of US dollars), and thus were rarely purchased by an individual. However, they were
much smaller, less expensive, and generally simpler to operate than many of the mainframe
computers of the time. Therefore, they were accessible for individual laboratories and research
projects. Minicomputers largely freed these organizations from the batch processing and
bureaucracy of a commercial or university computing center.
In addition, minicomputers were relatively interactive and soon had their own operating
systems. Eventually, the minicomputer included VAX and larger minicomputers from Data
General, Prime, and others. The minicomputer era largely was a precursor to personal computer
usage and an intermediary step from mainframes.
Development of the single-chip microprocessor was an enormous catalyst to the
popularization of cheap, easy to use, and truly personal computers. Arguably the first true "personal
computer" was the Altair 8800, which brought affordable computing to an admittedly select market
in the 1970s. However, it was arguably this computer that spawned the development of both Apple
Computer as well as Microsoft, spawning the Altair BASIC programming language interpreter,
Microsoft's first product. The first generation of microcomputers (computers based on a
microprocessor) that appeared in the mid-1970s, due to the success of the Steve Wozniak-designed
Apple Computer release, the Apple II, were usually known as home computers. These were less
capable and in some ways less versatile than large business computers of the day. They were
generally used by computer enthusiasts for learning to program, running simple office/productivity
applications, electronics interfacing, and general hobbyist pursuits.
It was the launch of the VisiCalc spreadsheet, initially for the Apple II (and later for the
Atari 8-bit family, Commodore PET, and IBM PC) that became the "killer app" that turned the
microcomputer into a business tool. This was followed by the August 1981 release of the IBM PC
which would revolutionize the computer market. The Lotus 1-2-3, a combined spreadsheet (partly
based on VisiCalc), presentation graphics, and simple database application, would become the PC's
own killer app. Good word processor programs would also appear for many home computers, in
particular the introduction of Microsoft Word for the Apple Macintosh in 1985 (while earlier
versions of Word had been created for the PC, it became popular initially through the Macintosh). In the January 3, 1983 issue of Time magazine the personal computer was named the "Machine of
the Year" or its Person of the Year for 1982. During the 1990s, the power of personal computers
increased radically, blurring the formerly sharp distinction between personal computers and multiuser
computers such as mainframes. Today higher-end computers often distinguish themselves from
personal computers by greater reliability or greater ability to multitask, rather than by brute CPU
ability.

Other

Mainframe operating systems, such as IBM's z/OS, and embedded operating systems such
as VxWorks, eCos, and Palm OS, are usually unrelated to Unix and Windows, except for Windows
CE, Windows NT Embedded 4.0 and Windows XP Embedded which are descendants of Windows,
and several *BSDs, and Linux distributions tailored for embedded systems. OpenVMS from
Hewlett-Packard (formerly DEC), is still under active development.
Older operating systems which are still used in niche markets include the Windows-like
OS/2 from IBM; Mac OS, the non-Unix precursor to Apple's Mac OS X; BeOS; RISC OS; and
AmigaOS.


Research and development of new operating systems continues. GNU HURD is designed to
be backwards compatible with Unix, but with enhanced functionality and a microkernel
architecture. Microsoft Singularity is a research project to develop an operating system with better
memory protection.

Microsoft Windows

The Microsoft Windows family of operating systems originated as a graphical layer on top of
the older MS-DOS environment for the IBM PC. Modern versions are based on the newer Windows
NT core that first took shape in OS/2 and borrowed from OpenVMS. Windows runs on 32-bit and
64-bit Intel and AMD computers, although earlier versions also ran on the DEC Alpha, MIPS, and
PowerPC architectures (some work was done to port it to the SPARC architecture).

As of 2004, Windows held a near-monopoly of around 90% of the worldwide desktop market share,
although this is thought to be dwindling due to the increase of interest focused on open source
operating systems. [1] It is also used on low-end and mid-range servers, supporting applications
such as web servers and database servers. In recent years, Microsoft has spent significant marketing and R&D money to demonstrate that Windows is capable of running any enterprise application (see
the TPC article).

Unix-like

The Unix-like family is a diverse group of operating systems, with several major subcategories
including System V, BSD, and Linux. The name "Unix" is a trademark of The Open
Group which licenses it for use to any operating system that has been shown to conform to the
definitions that they have cooperatively developed. The name is commonly used to refer to the large
set of operating systems which resemble the original Unix.
Unix systems run on a wide variety of machine architectures. They are used heavily as
server systems in business, as well as workstations in academic and engineering environments. Free
software Unix variants, such as Linux and BSD, are increasingly popular. They are used in the
desktop market as well, for example Ubuntu, but mostly by hobbyists.
Some Unix variants like HP's HP-UX and IBM's AIX are designed to run only on that
vendor's proprietary hardware. Others, such as Solaris, can run on both proprietary hardware and on
commodity x86 PCs. Apple's Mac OS X, a microkernel BSD variant derived from NeXTSTEP,
Mach, and FreeBSD, has replaced Apple's earlier (non-Unix) Mac OS. Over the past several years,
free Unix systems have supplanted proprietary ones in most instances. For instance, scientific
modeling and computer animation were once the province of SGI's IRIX. Today, they are
dominated by Linux-based or Plan 9 clusters.
The team at Bell Labs who designed and developed Unix went on to develop Plan 9 and
Inferno, which were designed for modern distributed environments. They had graphics built-in,
unlike Unix counterparts that added it to the design later. Plan 9 did not become popular because,
unlike many Unix distributions, it was not originally free. It has since been released under Free
Software and Open Source Lucent Public License, and has an expanding community of developers.
Inferno was sold to Vita Nuova and has been released under a GPL/MIT license.

Today

Command line interface (or CLI) operating systems can operate using only the keyboard for
input. Modern OS's use a mouse for input with a graphical user interface (GUI) sometimes
implemented as a shell. The appropriate OS may depend on the hardware architecture, specifically
the CPU, with only Linux and BSD running on almost any CPU. Windows NT has been ported to
other CPUs, most notably the Alpha, but not many. Since the early 1990s the choice for personal
computers has been largely limited to the Microsoft Windows family and the Unix-like family, of
which Linux and Mac OS X are becoming the major choices. Mainframe computers and embedded
systems use a variety of different operating systems, many with no direct connection to Windows or
Unix, but typically more similar to Unix than Windows.

• Personal computers
o IBM PC compatible - Microsoft Windows and smaller Unix-variants (like Linux and
BSD)
o Apple Macintosh - Mac OS X, Windows, Linux and BSD
• Mainframes - A number of unique OS's, sometimes Linux and other Unix variants.
• Embedded systems - a variety of dedicated OS's, and limited versions of Linux or other OS's

History of Operating Systems

An operating system (OS) is a software program that manages the hardware and software

resources of a computer. The OS performs basic tasks, such as controlling and allocating memory,

prioritizing the processing of instructions, controlling input and output devices, facilitating

networking, and managing files.

The first computers did not have operating systems. However, software tools for managing

the system and simplifying the use of hardware appeared very quickly afterwards, and gradually

expanded in scope. By the early 1960s, commercial computer vendors were supplying quite

extensive tools for streamlining the development, scheduling, and execution of jobs on batch

processing systems. Examples were produced by UNIVAC and Control Data Corporation, amongst

others.

Through the 1960s, several major concepts were developed, driving the development of

operating systems. The development of the IBM System/360 produced a family of mainframe

computers available in widely differing capacities and price points, for which a single operating

system OS/360 was planned (rather than developing ad-hoc programs for every individual model).

This concept of a single OS spanning an entire product line was crucial for the success of System/360 and, in fact, IBM's current mainframe operating systems are distant descendants of this original system; applications written for the OS/360 can still be run on modern machines. OS/360 also contained another important advance: the development of the hard disk permanent storage device (which IBM called DASD). Another key development was the concept of time-sharing: the idea of sharing the resources of expensive computers amongst multiple computer users interacting in real time with the system.

Time sharing allowed all of the users to have the illusion of having exclusive access to the machine; the Multics time sharing system was the most famous of a number of new operating systems developed to take advantage of the concept. Multics, particularly, was an inspiration to a number of operating systems developed in the 1970s, notably Unix. Another commercially-popular minicomputer operating system was VMS.

The first microcomputers did not have the capacity or need for the elaborate operating systems that

had been developed for mainframes and minis; minimalistic operating systems were developed.

One notable early operating system was CP/M, which was supported on many early

microcomputers and was largely cloned in creating MS-DOS, which became wildly popular as the

operating system chosen for the IBM PC (IBM's version of it was called IBM-DOS or PC-DOS), its

successors making Microsoft one of the world's most profitable companies. The major alternative

throughout the 1980s in the microcomputer market was Mac OS, tied intimately to the Apple

Macintosh computer.

By the 1990s, the microcomputer had evolved to the point where, as well as extensive GUI

facilities, the robustness and flexibility of operating systems of larger computers became

increasingly desirable. Microsoft's response to this change was the development of Windows NT,

which served as the basis for Microsoft's entire operating system line starting in 1999. Apple rebuilt

their operating system on top of a Unix core as Mac OS X, released in 2001. Hobbyist-developed

reimplementations of Unix, assembled with the tools from the GNU project, also became popular;

versions based on the Linux kernel are by far the most popular, with the BSD derived UNIXes

holding a small portion of the server market. The growing complexity of embedded devices has a growing trend to use embedded operating systems on them.

Introduction

Modern general-purpose computers, including personal computers and mainframes, have an
operating system to run other programs, such as application software. Examples of operating
systems for personal computers include Microsoft Windows, Mac OS (and Darwin), Unix, and
Linux.




The lowest level of any operating system is its kernel. This is the first layer of software loaded into memory when a system boots or starts up.

The kernel provides access to various common core services to all other system and application programs. These services include, but are not limited to: disk access, memory management, task scheduling, and access to other hardware devices.

As well as the kernel, an operating system is often distributed with tools for programs to
display and manage a graphical user interface (although Windows and the Macintosh have these
tools built into the operating system), as well as utility programs for tasks such as managing files
and configuring the operating system. They are also often distributed with application software that does not relate directly to the operating system's core function, but which the operating system distributor finds advantageous to supply with the operating system.

The delineation between the operating system and application software is not precise, and is
occasionally subject to controversy. From commercial or legal points of view, the delineation can
depend on the contexts of the interests involved. For example, one of the key questions in the
United States v. Microsoft antitrust trial was whether Microsoft's web browser was part of its
operating system, or whether it was a separable piece of application software.

Like the term "operating system" itself, the question of what exactly should form the
"kernel" is subject to some controversy, with debates over whether things like file systems should
be included in the kernel. Various camps advocate microkernels, monolithic kernels, and so on.
Operating systems are used on most, but not all, computer systems. The simplest computers,
including the smallest embedded systems and many of the first computers did not have operating
systems. Instead, they relied on the application programs to manage the minimal hardware
themselves, perhaps with the aid of libraries developed for the purpose. Commercially-supplied
operating systems are present on virtually all modern devices described as computers, from personal computers to mainframes, as well as mobile computers such as PDAs and mobile phones.