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Computer System Organization
Computer contains input devices (keyboard,
mouse, A/D (analog-to-digital) converter, etc.),
a computational unit, and output devices
(monitors, printers, D/A converters). The
computational unit is the computer's heart, and
usually consists of a central processing unit
(CPU), a memory, and an input/output (I/O)
Characteristics of Computer
• Speed - The speed of a computer is incredibly faster
than what man can possibly record or calculate
• Storage - A computer system can store a large
amount of data in a systematic manner.
• Accuracy and Reliability - Inspite of high speed, the
computers are quite accurate and reliable in their
calculations. the accuracy of operation of a computer
is always 100%.
• Automatic - Once the process has been initiated,
computer is quite capable of functioning
automatically. it does not require a prompt from an
operator at each stage of the process.
• Diligence/Endurance - Is capable of operating at
exactly the same level of speed and accuracy even if
it has to carry out the most voluminous and complex
operations for a long period of time.
• Scientific Approach - The entire approach to solving
problems is highly scientific, objective and
sequentially carried out, leaving no room for
emotional & subjective evaluations made by man.
• Versatility - The wide use of computers in so many
areas in day-to-day life is an ample evidence of its
Uses of Computer
• Word Processing - Word Processing software
automatically corrects spelling and grammar
• Medicine - You can diagnose diseases. You can learn
the cures.
• Mathematical Calculations - Computing speeds of
over a million calculations per second
• Banks - All financial transactions are done by
computer software. They provide security, speed and
• Travel - One can book air tickets or railway tickets
and make hotel reservations online.
• Examinations - Online exams and get instant
Generation of Computer
• First Generation (1940-1956) - The first computers
used vacuum tubes for circuitry and magnetic drums for
• Second Generation (1956-1963) - Transistors
replaced vacuum tubes and ushered in the second
generation of computers.
• Third Generation (1964-1971) - The development of
the integrated circuit was the hallmark of the third
generation of computers.
• Fourth Generation (1971-Present) - The
microprocessor brought the fourth generation of
computers, as thousands of integrated circuits we
rebuilt onto a single silicon chip.
Types of Computer
• Analog - Computer that uses the continuouslychangeable aspects of physical phenomena such as
electrical, mechanical, or hydraulic quantities to model
the problem being solved.
• Micro-computer - Computer with a microprocessor
as its central processing unit.
• Mini-computer - A class of multi-user computers
that lies in the middle range of the computing
spectrum, in between the largest multi-user systems
and the smallest single-user systems.
• Mainframe - Are computers used mainly by large
organizations for critical applications, typically bulk
data processing.
• Super computer - A mainframe computer that is
among the largest, fastest, or most powerful of those
available at a given time.
• Hybrid - Computers that exhibit features of analog
computers and digital computers.
Input Device - A hardware device that sends
information into the CPU.
• Keyboard - An input device which uses an
arrangement of buttons or keys.
• Mouse - A pointing device.
• Trackball - A pointing device consisting of a ball.
• Joystick - An input device consisting of a stick.
• Digitizing Tablet - A computer input device that allows
one to hand-draw images and graphics.
• Scanners - Device that optically scans images, printed
text, handwriting, or an object, and converts it to a
digital image.
• Digital Camera - A camera that takes video or still
photographs, or both, digitally by recording images
via an electronic image sensor.
• MICR - Type of font capable of recognition using
magnetically charged ink.
• OCR - The mechanical or electronic translation of
images of handwritten, typewritten or printed text
into machine-editable text.
• OMR - The process of capturing human-marked data
from document forms.
• Bar-Code Reader - An electronic device for reading
printed barcodes.
• Voice Recognition - Converts spoken words to text.
• Light Pen - A small, photosensitive device connected
to a computer and moved by hand over an output .
• Touch Screen - A monitor screen that can detect and
respond to something, such as a finger or stylus,
pressing on it.
Output Deice - Any peripheral that receives and displays
output from a computer.
Monitor - A device that displays images or symbols
generated by computers
Characteristics of Monitors:
• Resolution - T he number of distinct pixels in each
dimension that can be displayed.
• Dot Pitch - Is a specification for a computer display
that describes the distance between dots (sub-pixels)
of the same color on the screen.
• Refresh Rate - Is the number of times in a second
that display hardware draws the data.
• Size - Is measured diagonally from one corner of the
screen to another.
Types of Monitors
• CRT - Is a vacuum tube containing an electron gun
and a fluorescent screen, with internal or external
means to accelerate and deflect the electron beam,
used to create images in the form of light emitted
from the fluorescent screen.
• Flat Panel - encompass a growing number of
technologies enabling video displays that are lighter
and much thinner than traditional television and video
• LCD Monitor/screen - Is a thin, flat panel used for
electronically displaying information such as text,
images, and moving pictures.
A printer is a peripheral which produces a hard copy
of documents stored in electronic form.
• Daisy Wheel - A device used in some electric
typewriters and printers, consisting of printing
characters fixed at the ends of spokes on a wheel.
• Dot Matrix - Is a type of printer with a head that runs
back and forth, or in an up and down motion, on the
page and prints by impact, striking an ink-soaked
cloth ribbon against the paper.
• Inkjet - Is a type of printer that reproduces a digital
image by propelling variably-sized droplets of liquid or
molten material (ink) onto a page.
• Laser - Is a common type of printer that rapidly
produces high quality text and graphics on plain
• Line Printer - Is a form of high speed impact printer in
which one line of type is printed at a time.
• Plotters - Is a vector graphics printing device to print
graphical plots, that connects to a computer.
• Sound Card - Is a computer expansion card that
facilitates the input and output of audio signals to and
from a computer under control of computer programs.
• Speaker - An output device that produce sound.
Primary Memory
Secondary Memory
Storage Capacity - Limited
Storage Capacity – Larger
Volatile Memory
Non-Volatile Memory
Primary Devices : RAM, ROM Secondary Devices : Floppy
Disk, Hard Disk
Storage Devices
• Magnetic Tape, Cartridge Tape - Storage Medium that
is accessed and processed sequentially. Advantages:
Low cost, Portable. Disadvantages: Slow, no direct
process, must be labeled, environment problem.
• Hard disk drives - Non-volatile storage device.
Advantages : Unlimited Storage Capacity, Direct
Access, Portable, High data transfer rate, less
vulnerable to data corruption. Disadvantages :
• Floppy Disks - A data storage medium that is
composed of a disk of thin, flexible ("floppy")
magnetic storage medium encased in a square or
rectangular plastic shell. Advantages: Low cost,
Portable, easy to use. Disadvantages: Unreliability
• CD - A Compact Disc (CD) is an optical disc used
to store digital data. Advantages: Low cost,
Portable. Disadvantages: Limited space
• VCD - Is a standard digital format for storing
video on a Compact Disc. Advantages: Low cost,
Portable. Disadvantages: Limited space.
• CD-RW - A rewritable optical disc format used to
store digital data.
• Zip Drive - Is a medium-capacity removable disk
storage system
• DVD - Also known as Digital Versatile Disc or
Digital Video Disc, is an optical disc storage
media format. Its main uses are video and data
• DVD-RW - Is a rewritable optical disc.
Is a general term primarily used for digitally
stored data such as computer programs and
other kinds of information read and written by
• System Software - Computer software designed
to operate the computer hardware and to provide
and maintain a platform for running application.
• Application Software - Computer software
designed to help the user perform a particular
Operating System (OS)
Operating System acts as an interface between
hardware and user. It is responsible for the
management and coordination of activities and
the sharing of the resources of a computer.
• Single user OS - Usable by a single user at a time.
• Multi user OS - The operating systems of this type
allow a multiple users to access a computer system
• Real time OS - It is a multitasking operating system
that aims at executing real-time applications using
specialized scheduling algorithms.
• Timesharing OS - Is sharing a computing resource
among many users by means of multiprogramming
and multi-tasking By allowing a large number of users
to interact concurrently with a single computer
• Batch processing OS - Execution of a series of
programs ("jobs") on a computer without manual
• Multiprocessing OS - Use of two or more central
processing units (CPUs) within a single computer
• Multiprogramming OS - Allocation of a computer
system and its resources to more than one concurrent
application, job or user.
• Multitasking OS - A method by which multiple tasks,
also known as processes, share common processing
resources such as a CPU.
• Distributed processing - Distributed processing
implies that processing will occur on more than one
processor in order to complete a transaction.
Programming Language
• A programming language is an artificial language that can
be used to instruct a computer to do a particular task.
• Machine Language : Machine language is the language of '0'
and '1' which is actually understood by the machine and thus
no translator is required. But is not in readable form for
human being.
• A programming language is an artificial language that can
be used to instruct a computer to do a particular task.
• Machine Language : Machine language is the language of '0'
and '1' which is actually understood by the machine and thus
no translator is required. But is not in readable form for
human being.
• Assembly Language : Assembly Language is language which
is in symbolic codes for ex. If instruction of adding two
numbers has to be written 'ADD' symbol can be used in this
program can be written. Thus assembly language are a little
easier to code for human beings but a program called
assembler is needed to translate this symbolic code in
machine code.
• High Level Languages : High level languages
are in easily readable form and a program
called compiler is used to translate the
program into machine code.
• Compiler : It is a translator program which is
used to translate high level language program
to machine language program. Thus high
level language program acts as input for the
compiler and the machine language comes as
output from it. After compilation of the source
program, the resulting object program is
saved for further use, and thus repeated
compilation is not necessary
• Interpreter : It is also a type of translator program.
Unlike Compiler, which gives a machine code program
as a result, Interpreter only results in execution of
program if program's syntax is right but since the
resultant object program is not saved for further use
thus interpreter is needed every time the program is
Interpreter takes one statement of source program,
translates it into object program instruction and then
immediately executes the resulting machine language
instruction while compiler translates the entire source
program into object program and is then not involved
into the execution.
Assembler : Assembler is a translator program which
translates assembly language program into machine
language program. Along with translating, it also assembles
the machine language program in the main memory of the
computer and thus make it ready for the execution.
Scans complete
program and then
translate it into
machine code
When all the syntax
errors are removed,
only then program can
be executed
Slow Debugging
Fast Execution
Scan a single line,
translate it, and then
move to the next line
Every line is checked
for the syntax error
and then translated
into the machine code
Fast Debugging
Slow Execution