What is a Process?
A process is a computer program running on a computer.A computer
program in simple terms is an executable set of commands for the
computer to perform. A process is an actively running program which
may or may not be running in the background. A program running in
the background is one that the computer user may not be aware of,
but it may be providing useful services such as an ability to
connect to other computers.
THE CENTRAL PROCESSING UNIT
This is the brain of the computer; it reads and executes program
instructions, performs calculations, and makes decisions .The CPU
is responsible for storing and retrieving information on disks and
other media. It also handles information on from one part of the
computer to another like a central switching station that directs
the flow of traffic throughout the computer system.
DIFFERENT FACES OF A CPU
MAIN COMPONENTS OF CPU
WHAT DOES THE CPU DO?
Carries out instructions and tells the rest of computer system
what to do. Sends command signals to the other components of the
system. Perform arithmetic calculations and data manipulation.
Holds data and instructions, which are in current use.
CONTROL UNIT (CU) Directs the entire computer system to carry
out stored program instructions.
Instructs the arithmetic logic unit which arithmetic operations
or logical operation is to be performed.
ARITHMETIC LOGIC UNIT (ALU) Executes arithmetic and logical
operations. Arithmetic operations include addition, subtraction,
multiplication and division. Logical operations compare numbers,
letters and special characters.
Holds data and instructions for processing. RAM (Random Access
Memory) - used to store instructions and data needed while
processing. b) ROM (Read Only Memory) - ROM comes with instructions
permanently stored inside and these instructionscannot be
over-written by the computers CPU.
MICROPROCESSORA silicon chip that contains a CPU. In the world
of personal computers, the terms microprocessor and CPU are used
interchangeably.It's sometimes called a logic chip. It is the
"engine" that goes into motion when you turn your computer on.At
the heart of all personal computers and most workstations sits a
microprocessor. Microprocessors also control the logic of almost
all digital devices, from clock radios to fuel-injection systems
Three basic characteristics differentiate microprocessors:
Instruction set: The set of instructions that the microprocessor
can execute. bandwidth : The number of bits processed in a single
instruction. clock speed : Given in megahertz (MHz), the clock
speed determines how many instructions per second the processor can
MICROPROCESSOR (cont.)In both cases, the higher the value, the
more powerful the CPU. For example, a 32-bit microprocessor that
runs at 50MHz is more powerful than a 16-bit microprocessor that
runs at 25MHz.
In addition to bandwidth and clock speed, microprocessors are
classified as being either RISC (reduced instruction set computer)
or CISC (complex instruction set computer).
WHAT IS INPUT? Input is any data or instructions you enter into
the memory of a computer. Once input is in memory, the CPU can
access it and process the input into output. Four types of input
are data, programs, commands, and user responses.
4 TYPES OF INPUTData is a collection of unorganized facts that
can include words, numbers, pictures, sounds, and videos. A program
is a series of instructions that tells a computer how to perform
the tasks necessary to process data into information. Programs are
kept on storage media such as a floppy disk, hard disk, CD-ROM, or
4 TYPES OF INPUT (cont.) A command is an instruction given to a
computer program. Typing keywords or pressing special keys on the
keyboard can issue commands.A user response is an instruction you
issue to the computer by replying to a question posed by a computer
program, such as do you want to save the change you made?
INPUT DEVICESAn input device is any hardware component that
allows you to enter data, programs, commands, and user responses
into a computer. Input devices include the keyboard, pointing
devices, scanners and reading devices, digital cameras, audio and
video input devices for physically challenged user.
Many input devices use an electronic pen instead of keyboard or
mouse for input. Some of there devices require you to point to
onscreen objects with the pen ;others allow you to input data using
drawings, handwriting, and other symbols that are written with the
pen on a surface.
LIGHT PEN A light pen is a handheld input device that contains a
light source or can detect light. Some light pens require a
specially designed monitor, while others work with a standard
LIGHT PENInstead of touching the screen with your finger to
interact with the computer, you press the light pen against the
surface of the screen or point the light pen at the screen and then
press a button on the pen.
PEN COMPUTING Many handheld computers also allow inputting data
using an electronic pen (also called a stylus) looks like a
ballpoint pen but uses an electronic head instead of ink. Pen
computers use handwriting recognition software that translates the
letters and symbols used in handwriting into character data that
the computers can use.
GRAPHICS TABLET A graphics tablet, also called a digitizer or
digitizing tables, consists of a flat, rectangular, electronic
plastic bond used to input drawings, sketches, or other graphical
Each location on the graphical tablet corresponds to a specific
location on the screen. When you draw on the tablet with either an
electronic pen or a puck, the tablet detects and converts the
movements into digital signals that are sent into the computer.
TRACKBALLA mechanical mouse has ball mechanism on the bottom, a
trackball is a station- aryl pointing device with a ball mechanism
on its top . Although it shares characteristic with a mouse, a
trackball is not as accurate as a mouse .A trackballs ball
mechanism also requires frequent cleaning because it picks up oils
from your fingers and dust from the environment.
CAMERADigital camera allows you to take pictures and store the
photographed images digitally instead of on traditional film.
With some digital cameras, you download, or transfer a copy of,
the stored pictures to your computer by connecting a cable between
the digital camera and your computer and using special software
included with the camera.
The three basic types of digital cameras are studio cameras,
field cameras, and point-and shoot- cameras.
MOUSE The mouse is the most widely used pointing device because
it takes full advantage of a graphical user interface.
A mouse is an input device that is used to control the movement
of the pointer on the screen and to make selections from the
MOUSE TYPES A mouse that has a rubber or metal ball on its
underside is called a mechanical mouse. When the ball rolls in a
certain direction, electronic circuits in the mouse translate the
movement of the mouse into signals that are sent to the computer.
Another type of mouse, called an optical mouse, has no moving
mechanical parts inside; instead it uses devices that emit light to
detect the mouses movement.
SCANNERS Scanners have become an important part of the home
office over the last few years. Scanner technology is everywhere
and used in many ways:
Flatbed scanners, also called desktop scanners, are the most
versatile and commonly used scanners. In fact, this article will
focus on the technology as it relates to flatbed scanners.
SCANNERS (cont.)Sheet-fed scanners are similar to flatbed
scanners except the document is moved and the scan head is
immobile. A sheet-fed scanner looks a lot like a small portable
SCANNERS (cont.)Handheld scanners use the same basic technology
as a flatbed scanner, but rely on the user to move them instead of
a motorized belt. This type of scanner typically does not provide
good image quality. However, it can be useful for quickly capturing
SCANNERS (cont.)Drum scanners are used by the publishing
industry to capture incredibly detailed images. They use a
technology called a photo multiplier tube (PMT). In PMT, the
document to be scanned is mounted on a glass cylinder. At the
center of the cylinder is a sensor that splits light bounced from
the document into three beams. Each beam is sent through a color
filter into a photo multiplier tube where the light is changed into
an electrical signal.
KEYBOARD TYPESA standard computer keyboard sometimes is called a
QWERTY keyboard because of the layout of its typing area.
Pronounced KWER-tee, this keyboard layout is named after the
first six leftmost letters on the top alphabetic line of the
keyboard. Because of the way the keys are organized, a QWERTY
keyboard might limit your typing speed.
KEYBOARD TYPES (cont.)A keyboard with an alternative layout was
designed to improve typing speed called the Dvorak keyboard
This type of keyboard places the most frequently typed letters
in the middle of the typing area.
Despite the more logical design of the Dvorak keyboard, the
QWERTY keyboard is more widely used.
MICROPHONEA microphone is used to record sound. The sound is
then saved as a sound file on the computer.
JOYSTICKUsers running game software such as a driving of flight
simulator may prefer to use a joystick as their pointing
A joystick is a vertical lever mounted on a base. You move the
lever in different direction to control the actions of a vehicle or
player. The lever usually includes buttons called triggers that you
can press to activate certain events.
WHAT IS OUTPUT?0utput is data that has been processed into a
useful form called information.
Computers generate several types of output, depending on the
hardware and software being used and the requirements of the user.
You may choose to display or view this output on a monitor, print
it on a printer, or listen to it through speakers or a headset.
4 COMMON TYPES
TEXTConsists of characters that are used to create words,
sentences, and paragraphs. A character is a letter, number,
punctuation mark, or any other symbol that requires one byte of
computer storage space.
GRAPHICSAre digital representations of non-text information such
as drawings, charts, and photographs. Graphics also can be
animated, giving them the illusion of motion.
AUDIOIs music, speech, or any other sound. Recall that sound
waves, such as the human voice or music, are analog. To store such
sounds, a computer converts the sounds from a continuous analog
signal into a digital format. Most output devices require that the
computer convert the digital format back into analog signals.
VIDEOVideo consists of images that are played back at speeds
that provide the appearance of full motion. Video often is captured
with a video input devices such as a camera or VCR. A video capture
card converts an analog video signal into a digital that a computer
can understand. The digital signal then is stored on the computers
OUTPUT DEVICESAn output device is any computer component capable
of conveying information to a user. Commonly used output devices
include display devices, speakers, headset, data projector,
facsimile machines and multifunction devices.
DATA PROJECTORSA data projector takes the image that displays on
a computer screen and projector it into a screen so that an
audience of people can see the image clearly. Data projectors can
be large devices attached to ceiling or wall in an auditorium, or
they can be small portable devices. Two types of smaller,
lower-cost units are LCD projectors and DLP projectors.
LIQUID CRYSTAL DISPLAYAn LCD projector, which uses liquid
crystal display technology, attaches directly to a computer and
uses its own light source to display the information shown on the
computer screen. Because LCD projectors tend to produce
lower-quality images, some users prefer to use a DLP projector for
shaper, brighter images. A liquid crystal display consists of an
array of tiny segments (called pixels) that can be manipulated to
DIGITAL LIGHT PROCESSING (DLP)A digital light processing (DLP)
projectors uses tiny mirrors to reflect light, producing crisp,
bright, colorful images that remain in focus and can be seen
clearly even in a well-lit room.
CRT MONITORSA CRT monitor, or monitor is a display device that
consists of a screen housed in a plastic or metal case.
A color monitor display text, graphics and video information in
color. Color monitor are used widely with all types of computers
because most of todays software is designed to display information
CRT MONITORS (cont.)Monitor that display only one color are
considered monochrome. A monochrome monitor display text, graphics
and video information in one color (usually white, amber or green)
on a black background.
Like a television set, the core of a CRT monitor is a large
glass tube called a cathode ray tube (CRT).
MONITORThe computer monitor, screen or VDU (visual Display Unit)
is the most common output devices. Screen sizes are measured
diagonally and are still quoted in inches. Larger monitor make
working at a computer easier on the eyes and are essential for use
in DTP (Desktop Publishing) and CAD work.
MONITOR (cont.)ADVANTAGERelatively cheap and reliable, can
display text and graphics in a wide range of colors. They are also
quiet and do not waste paper.
DISADVANTAGE No permanent copy to keep and unsuitable for users
with visual problems.
GAS PLASMA MONITORS Gas plasma monitors use gas plasma
technology, which substitutes a layer of gas the liquid crystal
material in an LCD monitor. When voltage is applied, the gas glows
and produces the pixels that form an image. Gas plasma monitors
offer larger screen sizes and higher display quality than LCD
monitors but are much more expensive.
MONITOR QUALITYThe quality of a monitors display depends largely
Resolution. The resolution or sharpness and clarity, of a
monitor are related directly to the number of pixels it can
display. Resolution is expressed as two separate numbers: the
number of columns of pixels and the number of rows of pixels a
monitor can display.
Dot pitch. Pitch is a measure of image clarity. The dot pitch is
the vertical distance between each pixel on a monitor. The smaller
the distance between the pixels, the sharper the displayed
Refresh rate. A monitors refresh rate should be fast enough to
maintain a constant, flicker-free image. A slower refresh rate
causes the image to fade and then flicker as it is redrawn, which
can headaches for user. Refresh rate is measured according to
hertz, which is the number of times per second the screen is
High-definition television (HDTV) is a type of television set
that works with digital broadcasting signals and support a wider
screen and higher resolution display than a standard television
set. When you use a standard television set as a monitor for your
computer, the output must be converted to an analog signal that can
be displayed by the television set.
Printers are primary output devices used to generate information
from the computers. These output are often referred to as Hard
Copies or Printout in computer jargon.Character printers are the
slowest printers since they print character by character. There are
two types of character printers: Dot-Matrix printers
DOT-MATRIX PRINTERINK JET PRINTERLASER PRINTER
TYPES OF PRINTERS
DOT-MATRIX PRINTERS Limited to situations where carbon copies
are needed and the quality is not too important. Typical uses might
be in warehouse where duplicate copies of orders need to produce
quickly and cheaply. The printing quality is low because of this
impact these printers can be quite noise. The purchase cost is low
and the running costs are very low. Can print fairly quickly, if
you remember that multiple copies are being printed in one print
run. Robust and can operate in harsh environments. If several
sheets of self-carbonating paper are placed into the printer then
the impact will produce multiple copies.
TYPES OF PRINTERS(cont.)INK-JET PRINTA popular choice for home
and school use where small amounts of printing are done The ink
cartridges can be expensive so running costs can be high. Speed is
slow compared to a laser printer.Relatively inexpensive and produce
high quality black and white or color printing.
TYPES OF PRINTERS(cont.)LASER PRINTERSCommon wherever fast, high
quality printing is required. Non color laser printers are more
expensive than ink-jet printers (but thedifference is narrowing).
Color laser printers are considerably more expensive (but their
speed and high quality output means they are becoming more
popular). Quiet and fast and produce high quality printouts.
Running cost are low because although toner cartridges are
expensive to replace, they last a long time.
SPEAKER A system's speaker is the component that takes the
electronic signal stored on things like CDS, Tapes, and DVDs and
turns it back into actual sound that we can hear.
A device that draws pictures on paper based on commands from
computer. Plotter differs from printer in that they draw lines
using a pen. Multicolor plotter use different colored pens to draw
FACSIMILE (FAX) MACHINE A facsimile (fax) machine is a device
that transmits and receives documents overtelephone lines. The
documents can contain text, drawings, or photographs, or can
behandwritten. When sent or received via a fax machine, these
documents are known as faxes.
WHAT IS STORAGE?Storage also called secondary storage, auxiliary
storage, or mass storage. Holds items such as data, instruction,
and information for future use. Think of storage as a filling
cabinet used to hold file folder, and memory as the top of your
desk. When you need to work with a file, you remove it from the
filling cabinet (storage) and place it on your desk (memory). When
you are finished with the file, you return it to the filling
WHAT IS STORAGE? (cont.)Storage devices can function as sources
of input and output. For example, each time a storage devices
transfer data, instruction, and information from a storage medium
into memory-a process called reading-it function as an input
source. When a storage device transfer these item from memory to a
storage medium-a process called writing-it function as an output
WHAT IS STORAGE? (cont.)The size, or capacity, of storage
devices, is measured by the number of bytes (characters). For
example, a typical floppy disk can store 1.44 MB of data
(approximately 1,440,000 bytes) and a typical hard disk can store
8GB of data (approximately 8,000,000,000 bytes).
Memory, which is composed of one or more chips on the
motherboard, holds data and instruction while the CPU is processing
them. The two basic type of memory are volatile and nonvolatile.
The contents of volatile memory, such as RAM are lost (erased) when
the power to the computer is turned of. The contents of nonvolatile
memory, however, are not lost when power is removed from the
computer. For example, once instruction has been record onto a
nonvolatile ROM chip, they usually cannot be erased or change, and
the contents of the chips are not erased when power is turned
A floppy disk, or diskette, is a portable, inexpensive storage
medium that consists of a thin, circular, flexible plastic disk
with a magnetic coating enclosed in a square-shaped plastic
In the early 1970s, IBM introduced the floppy disk a new type or
storage. Because these early 8-inch wide disk had flexible plastic
cover, many users referred to them as floppies. The next generation
of floppies looked much the same, but was only 5.25-inches wide.
Today, the most widely used floppy disk is 3.5-inches wide. The
flexible cover of the earlier floppy disk has been replaced with a
rigid plastic outer cover. Thus, although todays 3-5 inches disk
are not at all floppy. The term floppy disk still used.
CHARACTERISTICS OF A FLOPPY DISK
To protect them from accidentally being erased, floppy disk have
a write-protect notch. A write-protect notch is a small opening in
the corner of the floppy disk with a tab that you slide to cover or
expose the notch.
CHARACTERISTICS OF A FLOPPY DISK(cont.)On a floppy disk, if the
write protect notch is exposed, or open, the drive cannot write on
the floppy disk. If the write-protect north is covered, or closed,
the drive can write on the floppy disk. The write protect notch
only affect the flopper disk drives capability of writing on the
disk: a floppy disk drive car read from the floppy disk whether the
write-protect notch is open or closed. Some floppy disk has a
second opening on the opposite side of disk that does not have the
small tab: this opening identifies the disk as a high-density
FLOPPY DISK DRIVE
A floppy disk drive (FDD) is a device that can read from and
write on a floppy disk. Desktop personnel computers usually have a
floppy disk drive installed inside the system unit.Floppy disk
drive is downward compatible, which means they recognize and can
use earlier media. Floppy disk drive is not upward compatible,
however, which means they cannot recognize newer media. For
example, a lower-density floppy disk drive cannot read from or
write on a high-density floppy disk.
FLOPPY DISK DRIVE(cont.)On any 3.5-inch floppy disk, a piece of
metal called the shutter covers an opening in the rigid plastic
shell. When you insert a floppy disk into a floppy disk drive, the
drives slides shutter to the side to expose a portion of both sides
of the floppy disks recording surface.
The read/write head is the mechanism that actually read items
from a write items on the floppy disk. Figure 6-0 illustrates the
steps for reading from and writing on a floppy disk. The average
access time for current floppy disk drives to locate an item on the
disk is 84 ms, or approximately 1/12 of a second.
A hard disk usually consist of several inflexible, circular
disk, called platter, on which item are stored electronically.
The hard disk in most desktop personnel computer is housed
inside the system unit. Such hard disk, which are not portable, are
considered fixed disk.A platter in a hard disk is made of aluminum,
glass, or ceramic and is coated with a material that allow item to
be magnetically recorded on it surface. On hard disk, the platter,
the read/write heads, and the mechanism for moving the heads across
the surface of the disk enclosed in a airtight, sealed case that
protect the platters from contamination.