by ALI ZAMIN FROM PAK

3.  Computer hardware equals the collection of physical
elements that comprise a computer system. Computer
hardware refers to the physical parts or components
of a computer such as monitor, keyboard, hard drive
disk, mouse, printers, graphic cards, sound
cards, memory, motherboard and chips, etc all of
which are physical objects that you can actually touch.
In contrast, software is untouchable. Software exists
as ideas,application, concepts, and symbols, but it
has no substance. A combination of hardware and
software forms a usable computing system.

7. A flat board with grids of buttons which are programmed to input characters
into the computer. Keyboards can be classified into different categories
based on their layout, connection type, form factor etc. The most common
keyboard layout is QWERTY which has been adopted from the typewriter. A
standard keyboard includes about 100 keys, each of which sends a different
signal to the CPU. It is connected to the computer through a PS/2 or an USB
port. Wireless keyboards use wireless technologies to communicate. Most
commonly used technologies are: Infrared, Radio frequencies and Bluetooth

8. V
A pointing device that detects two dimensional motions on a surface and sends the
signal to the CPU. A mouse has two or more buttons and scroll wheels to allow users
to interact with the GUI. The traditional PC mouse has two buttons, while the traditional
Macintosh mouse has one button. Mouse with more than two buttons can be
programmed for specific tasks like short cut, launch application etc. The scroll wheel is
used for vertical and horizontal scrolling. A mouse helps the user to have the ability to
perform various functions such as opening a program or file and does not require the
user to memorize commands.
Mice can be classified into two different types: Ball and Optical. Ball mice are
older technology and almost obsolete. This type of mouse has ball and wheel
mechanism which detects the motion and sends signal to the CPU. The optical
mouse does not use any wheel mechanism for motion detection. Instead it uses a
light and a small optical sensor to detect the motion of the mouse by tracking a
tiny image of the desk surface. Optical mice avoid the problem of a dirty mouse
ball, which causes regular mice to roll unsmooth if the mouse ball and internal
rollers are not cleaned frequently.

9. Trackballs are similar to mice except that the ball is bigger, remains
stationary on the desk unlike mouse and it is located on the top. The
user uses fingers to roll the trackball and internal rollers sense the
motion which is transmitted to the computer. Trackballs have the
advantage over mice in that the body of the trackball remains
stationary on the desk and doesn’t need as much room as the mice.
Early laptop computers often used trackballs. Track balls are used
for special purposes such as air traffic control room, radar console
etc.

10. Touch screens are touch sensitive displays which can detect location of touches within
the touch sensitive display. There are three basic systems that are used to recognize a
person's touch:
1)Resistive
2)Capacitive
3)Surface acoustic wave

11. The resistive system consists of a normal glass panel that is covered with a conductive
and a resistive metallic layer. These two layers are separated by thin space, and at the
top a scratch-resistant layer is placed. An electrical current runs through the two layers
while the monitor is operational. When a user touches the screen, it causes a change in
the electrical current which is identified as a touch event and sent to the controller
present inside the circuit board for processing. Once the coordinates are known, a
special driver translates the touch into something that the operating system can
understand, similar to the computer mouse “click”.
In the capacitive system, a layer that stores electrical charge is placed on the glass
panel of the monitor. The human body also carries electric charge. When a user touches
the monitor with his or her finger, some of the charge is transferred to the user, so the
charge on the capacitive layer decreases. This fluctuation of current is measured by the
circuit which is present at each corner of the display. The computer calculates, from the
relative differences in charge at each corner, exactly where the touch event took place
and then relays that information to the touch-screen driver software.
On the monitor of a surface acoustic wave system, two transducers (one receiving
and one sending) are placed along the X and Y axes of the monitor's glass plate.
Ultrasonic waves pass over the screen. . When the screen is touched, a portion of the
wave is absorbed by the object or user. This change in the ultrasonic waves register’s
the position of the touch event and sends this information to the controller for
processing

12. This is a devices that scans the printed materials and convert it into a digital form. The
scanner uses light to detect printed objects on paper. In case of a typical flatbed
scanner, the document is placed face-down on a glass bed. A moving optical mechanism
consisting of a lamp, a mirror and a lens moves back and forth underneath the glass.
The image sensor may be a CCD (Charged coupled device) or a CIS (Compact Image
Sensor), a single row of sensor elements mounted very close to the document. Light
from the lamp bounces off the document and then through a set of optical mechanisms it
is focused into the CCD. In the case of the CIS, the light and dark areas are picked up
directly by the sensor. The CCD/CIS digitizes the results via an analog-to-digital
converter, and sends the resulting information to the scanner's own hardware and then
to the host PC.

19. Computer software, or just software, is a
collection of computer programs and related
data that provides the instructions for telling
a computer what to do and how to do it.
Software refers to one or more computer
programs and data held in the storage of the
computer. In other words, software is a set of
programs, procedures, algorithms and its
documentation concerned with the operation
of a data processing system. Program
software performs the function of the
program it implements, either by directly
providing instructions to the digital
electronics or by serving as input to another
piece of software. The term was coined to
contrast to the old term hardware (meaning
physical devices). In contrast to
hardware, software "cannot be touched"

20. System software is computer software or an operating system designed to
operate and control the computer hardware and to provide a platform for
running application software.[
Application software is computer software designed to help the user to perform
specific tasks. Examples include enterprise software, accounting software,
office suites, graphics software and media players

21. A component or peripheral device (such as a barcode reader, graphic tablet, keyboard.
Input devices convert the user's actions and analog data (sound, graphics, pictures)
into digital electronic signals that can be processed by a computer.
An output device is any piece of computer hardware equipment used to communicate
the results of data processing carried out by an information processing system (such as a
computer) which converts the electronically generated information into human-readable
form..
The system unit, also known as a "tower" or "chassis," is the main part of a desktop
computer. It includes the motherboard, CPU, RAM, and other components. The system
unit also includes the case that houses the internal components of the computer.
The term "system unit" is often used to differentiate between the computer and
peripheral devices, such as the monitor, keyboard, and mouse.

22. In computer architecture, a bus is a subsystem that transfers data
between components inside a computer, or between computers.
Early computer buses were parallel electrical wires with multiple
connections, but the term is now used for any physical
arrangement that provides the same logical functionality as a
parallel electrical bus. Modern computer buses can use both
parallel and bit serial connections, and can be wired in either a
multidrop (electrical parallel) or daisy chain topology, or connected
by switched hubs, as in the case of USB.

23. These buses carry data from one unit to other, it is a bi-directional
bus i.e the data can be carried in both directions.
These buses carry address given by the CPU from one unit to
another in the computer.
These buses carry control signal from ALU to memory and from
memory to alu and then to the output unit.

24. The main memory of the computer is also known as
RAM, standing for Random Access Memory. It is
constructed from integrated circuits and needs to
have electrical power in order to maintain its
information. When power is lost, the information is
lost too! It can be directly accessed by the CPU.
The access time to read or write any particular byte
are independent of whereabouts in the memory that
byte is, and currently is approximately 50
nanoseconds (a thousand millionth of a second).
This is broadly comparable with the speed at which
the CPU will need to access data. Main memory is
expensive compared to external memory so it has
limited capacity. The capacity available for a given
price is increasing all the time. For example many
home Personal Computers now have a capacity of
16 megabytes (million bytes), while 64 megabytes
is commonplace on commercial workstations. The
CPU will normally transfer data to and from the main
memory in groups of two, four or eight bytes, even if
the operation it is undertaking only requires a single
byte.

26. Secondary memory is a type of computer
memory that is not directly accessed by the
central processing unit (CPU) of a computer
and is usually available as non-volatile
memory. One of the most common forms of
this memory is the hard drive of a
computer, which is used to store the operating
system (OS) and other programs. Other forms
of secondary memory include disc drives for
compact discs (CDs) or digital versatile discs
(DVDs), as well as removable flash memory.
In contrast to this, primary memory is
computer memory directly accessed by the
CPU, usually volatile memory, and tertiary
memory refers to systems outside of a
computer that can be directly accessed
through various means

30. The primary computer storage device. Like tape, it is magnetically recorded and can be
re-recorded over and over. Disks are rotating platters with a mechanical arm that moves
a read/write head between the outer and inner edges of the platter's surface. It can take
as long as one second to find a location on a floppy disk to as little as a couple of
milliseconds on a fast hard disk. See hard disk for more details.
Tracks and Spots
The disk surface is divided into concentric tracks (circles within circles). The thinner the
tracks, the more storage. The data bits are recorded as tiny magnetic spots on the
tracks. The smaller the spot, the more bits per inch and the greater the storage.
Sectors
Tracks are further divided into sectors, which hold a block of data that is read or written
at one time; for example, READ SECTOR 782, WRITE SECTOR 5448. In order to
update the disk, one or more sectors are read into the computer, changed and written
back to disk. The operating system figures out how to fit data into these fixed spaces.
Modern disks have more sectors in the outer tracks than the inner ones because the
outer radius of the platter is greater than the inner radius (see CAV). See magnetic tape
and optical disc.

32. Random-access memory (RAM) is a form of computer data storage. A random-access
device allows stored data to be accessed in very nearly the same amount of time for any
storage location, so data can be accessed quickly in any random order. In
contrast, other data storage media such as hard disks, CDs, DVDs and magnetic
tape, as well as early primary memory types such as drum memory, read and write data
only in a predetermined order, consecutively, because of mechanical design limitations.
Therefore the time to access a given data location varies significantly depending on its
physical location.
Today, random-access memory takes the form of integrated circuits. Strictly
speaking, modern types of DRAM are not random access, as data is read in
bursts, although the name DRAM / RAM has stuck. However, many types of
SRAM, ROM, OTP, and NOR flash are still random access even in a strict sense. RAM
is often associated with volatile types of memory (such as DRAM memory
modules), where its stored information is lost if the power is removed. Many other types
of non-volatile memory are RAM as well, including most types of ROM and a type of
flash memory called NOR-Flash. The first RAM modules to come into the market were
created in 1951 and were sold until the late 1960s and early 1970s.