Hardware
An
exploded view of a personal computer and peripherals (some of which are optional):
Computer hardware
is a comprehensive term for all physical parts of a computer, as
distinguished from the data it contains or operates on, and the software
that provides instructions for the hardware to accomplish tasks. The
boundary between hardware and software has become blurred, with the
existence of
firmware
that is software "built into" the hardware. For example, a 2010-era LCD
display screen contains a small computer inside. Mass-market consumer
computers use highly standardized components and so are simple for an
end user
to assemble into a working system. Most 2010s-era computers only
require users to plug in the power supply, monitor, and other cables. A
typical
desktop computer consists of a
computer case (or "tower"), a metal chassis that holds the
power supply,
motherboard,
hard disk drive, and often an
optical disc drive. Most towers have empty space where users can add additional components. External devices such as a
computer monitor or
visual display unit,
keyboard, and a
pointing device (
mouse) are usually found in a personal computer.
The
motherboard connects all processor, memory and peripheral devices together. The
RAM, graphics card and processor are in most cases mounted directly onto the motherboard. The
central processing unit (microprocessor chip) plugs into a
CPU socket,
while the memory modules plug into corresponding memory sockets. Some
motherboards have the video display adapter, sound and other peripherals
integrated onto the motherboard, while others use
expansion slots for graphics cards, network cards, or other
I/O devices. The graphics card or sound card may employ a
break out box to keep the analog parts away from the
electromagnetic radiation
inside the computer case. Disk drives, which provide mass storage, are
connected to the motherboard with one cable, and to the power supply
through another cable. Usually, disk drives are mounted in the same case
as the motherboard; expansion chassis are also made for additional disk
storage.
For large amounts of data, a
tape drive
can be used or extra hard disks can be put together in an external
case. The keyboard and the mouse are external devices plugged into the
computer through connectors on an I/O panel on the back of the computer
case. The monitor is also connected to the input/output (I/O) panel,
either through an onboard port on the motherboard, or a port on the
graphics card. Capabilities of the personal computers hardware can
sometimes be extended by the addition of
expansion cards connected via an expansion
bus. Standard peripheral buses often used for adding expansion cards in personal computers include
PCI,
PCI Express (PCIe), and
AGP
(a high-speed PCI bus dedicated to graphics adapters, found in older
computers). Most modern personal computers have multiple physical PCI
Express expansion slots, with some of the having PCI slots as well.
Computer case
An empty
ATX case lying on its side
A computer case is an enclosure that contains the main components of a
computer. They are usually constructed from
steel or
aluminum combined with
plastic, although other materials such as
wood and
tempered glass
have been used for specialized units. Cases are available in different
sizes and shapes; the size and shape of a computer case are usually
determined by the configuration of the
motherboard
that it is designed to accommodate since this is the largest and most
central component of most computers. The most popular style for desktop
computers is
ATX, although
microATX and similar layouts became very popular for a variety of uses. Companies like
Shuttle Inc. and
AOpen have popularized small cases, for which
FlexATX is the most common motherboard size. In the 1990s, desktop computer cases were larger and taller than 2010-era computer cases.
Power supply unit
The power supply unit (PSU) converts general-purpose
mains AC electricity to
direct current
(DC) for the other components of the computer. The rated output
capacity of a PSU should usually be about 40% greater than the
calculated system power consumption needs to be obtained by adding up
all the system components. This protects against overloading the supply,
and guards against performance degradation. Power supply capacities
range from 250 to 2000
watts for desktop computers.
Processor
The
central processing unit (CPU) is a part of a computer that executes instructions of a software
program. In newer PCs, the CPU contains over a million transistors in one integrated circuit chip called the
microprocessor. In most cases, the processor plugs directly into the motherboard. The processor chip may have a
heat sink and a fan attached for cooling. A large number of computers today
[53] are suited to run an
x86-compatible microprocessor
[54] manufactured by
Intel,
AMD, or
VIA Technologies.
Motherboard
A
motherboard without processor, memory and expansion cards, cables
The motherboard, also referred to as system board or main board, is the primary
circuit board
within a personal computer, and other major system components plug
directly into it or via a cable. A motherboard contains 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 (often called boot
firmware or, in IBM PC compatible computers, a
BIOS or
UEFI).
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.
Main memory
A PC's main memory is a fast
primary 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 is used depends on
cost/performance issues at any particular time. Main memory is much
faster than mass storage devices like
hard disk drives or
optical discs, but is usually
volatile,
meaning that 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. As a result, main memory is generally not
suitable for long-term or archival data storage.
Storage drive
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 drive.
If the mass storage controller provides additional ports 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,
SATA and
SCSI. Solid state drives (
SSDs)
are a much faster replacement for traditional mechanical hard disk
drives but are also more expensive in terms of cost per gigabyte. Solid
state drives connect using several connectors, including SATA,
M.2, and
U.2. Some models use the
NVMe protocol, which have vastly improved performance over standard hard disk drives and older SSDs that use the older
AHCI protocol.
Visual display unit
A visual display unit, computer monitor or just display, is a piece of
electrical equipment, usually separate from the computer case, which displays visual
images without producing a permanent computer record. A display device was usually either a
CRT in the 1980s, but by the 2000s, flat panel displays such as a
TFT LCD had largely replaced the bulkier, heavier CRT screens.
Multi-monitor
setups are quite common in the 2010s, as they enable a user to display
multiple programs at the same time (e.g., an email inbox and a word
processing program). The display unit
houses an
electronic circuitry that generates its picture from
signals received from the computer. Within the computer, either integral to the motherboard or plugged into it as an
expansion card, there is pre-processing circuitry to convert the microprocessor's output
data
to a format compatible with the display unit's circuitry. The images
from computer monitors originally contained only text, but as
graphical user interfaces
emerged and became common, they began to display more images and
multimedia content. The term "monitor" is also used, particularly by
technicians in
broadcasting television, where a picture of the broadcast data is displayed to a highly standardized
reference monitor for confidence checking purposes.
Video card
The
video card—otherwise
called a graphics card, graphics adapter or video adapter—processes the
graphics output from the motherboard and transmits it to the display.
It is an essential part of modern multimedia-enriched computing.
Graphics circuitry may be integrated with the motherboard, or may be on
cards istalled in
PCI,
AGP, or
PCI Express
slots. When the IBM PC was introduced, most existing business-oriented
personal computers used text-only display adapters and had no graphics
capability. Home computers at that time had graphics compatible with
television signals, but with low resolution owing to the limited memory
available to the eight-bit processors available at the time.
Keyboard
A
"Model M" IBM computer keyboard from the early 1980s. Commonly called the "Clicky Keyboard" due to its
buckling spring key spring design, which gives the keyboard its iconic 'click' sound with each keystroke.
A
keyboard
is an arrangement of buttons that each correspond to a function,
letter, or number. They are the primary devices used for 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 keys specific to an operating system. 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. In addition to the
alphabetic keys found on a typewriter, computer keyboards typically have
a numeric keyboard and a row of
function keys and special keys, such as
CTRL,
ALT,
DEL and
Esc
Many keyboards include LED lights under the keys that increase the visibility of the letters or symbols in dark environments.
Mouse
A selection of computer mice built between 1986 and 2007
A computer
mouse
is a small handheld device that users hold and slide across a flat
surface, pointing at various elements of a graphical user interface with
an on-screen
cursor, and selecting and moving objects using the mouse buttons. Mice may be plugged into a dedicated mouse socket, or a
USB
port, or, may be connected wirelessly. Mice include one or more buttons
to allow a user to signal the computer to carry out some operation,
such as selecting an item from a menu of choices on the screen. A mouse
may have a scroll wheel, to allow users to move the displayed image. The
scroll wheel can also be pressed down, and 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, etc. These functions may be also
user-defined through software utilities. Mechanical mice used a ball,
which drove pulse generators to detect movement along "north-south" or
"east-west" axies. Optical mice use a special mouse pad with a printed
grid to allow detection of motion, or else use an imaging chip that
allows detection of motion on almost any opaque surface.
Other components
A proper ergonomic design of a personal computer workplace is necessary
to prevent repetitive strain injuries, which can develop over time and
can lead to long-term disability.
[55]
All computers require either fixed or removable storage for their operating system, programs and user-generated material. Early
home computers used
compact audio cassettes
for file storage; these were at the time a very low cost storage
solution, but were displaced by floppy disk drives when manufacturing
costs dropped, by the mid-1980s. Initially, the 5.25-inch and 3.5-inch
floppy drives
were the principal forms of removable storage for backup of user files
and distribution of software. As memory sizes increased, the capacity of
the floppy did not keep pace; the
Zip drive
and other higher-capacity removable media were introduced but never
became as prevalent as the floppy drive. By the late 1990s, the
optical drive, in
CD and later
DVD and
Blu-ray Disc
forms, became the main method for software distribution, and writeable
media provided means for data backup and file interchange. As a result,
floppy drives became uncommon in desktop personal computers since about
2000, and were dropped from many laptop systems even earlier.
[note 1]
A second generation of tape recorders was provided when
videocassette recorders
were pressed into service as backup media for larger disk drives. All
these systems were less reliable and slower than purpose-built magnetic
tape drives. Such tape drives were uncommon in consumer-type personal
computers but were a necessity in business or industrial use.
Interchange of data such as photographs from digital cameras is greatly
expedited by installation of a
card reader, which is often compatible with several forms of
flash memory devices. It is usually faster and more convenient to move large amounts of data by removing the card from the
mobile device, instead of communicating with the mobile device through a
USB interface.
A
USB flash drive performs much of the data transfer and backup functions formerly done with floppy drives,
Zip disks
and other devices. Mainstream operating systems for personal computers
provide built-in support for USB flash drives, allowing interchange even
between computers with different processors and operating systems. The
compact size and lack of moving parts or dirt-sensitive media, combined
with low cost and high capacity, have made USB flash drives a popular
and useful accessory for any personal computer user.
The
operating system can be located on any storage, but is typically installed on a hard disk or solid-state drive. A
Live CD
represents the concept of running an operating system directly from a
CD. While this is slow compared to storing the operating system on a
hard disk drive, it is typically used for installation of operating
systems, demonstrations, system recovery, or other special purposes.
Large flash memory is currently more expensive than hard disk drives of
similar size (as of mid-2014) but are starting to appear in laptop
computers because of their low weight, small size and low power
requirements. Computer communications involve
internal modem cards,
modems,
network adapter cards, and
routers. Common
peripherals and adapter cards include
headsets,
joysticks,
microphones,
printers,
scanners,
sound adapter cards (as a separate card rather than located on the motherboard),
speakers and
webcams.
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