Chapter 5. computer system

Chapter 5.
Computer System
Reference: Sunrise Computer Science XI
Lecture by: Er. Ashish K.C

Definition:
● The computer along with various hardware units and software that
makes the computer function and performs the different tasks is
collectively known as computer system.

Components of Computer System:
1. Hardware (Physical parts)
2. Software ( Logical parts)
3. Data
4. User

Concept of Computer Architecture:

Definition:
● The basic fundamental operational structure of computer system
organized according to different parts is known as computer
architecture or computer organization.

● At first, data are
transferred from input
devices or memory device
to the processor to
perform the certain
operation and retained in
primary memory.

● The processor then performs
the related operations on such
data from primary memory
and returns the result of
processing against to the
same memory location.

● While processing data
there is direct involvement
of control unit and
according to its instruction
the ALU performs the
required operation and the
information again turned to
the main memory

● From the main memory
the information may go
to the output section or
secondary storage for
current or future
purpose.

● Again data may be opened
or taken from secondary
storage for future
processing or modification.

● During the all logical
operation the control unit
controls the entire
components including
ALU, main memory,
Input/Output, primary/
secondary memory, etc.

Computer Hardware:
● The physical or tangible parts used in the computer system which can
be seen, touched and felt are known as computer hardware.
● It consists of electronic circuits and all the devices used to perform
various functions in the computer system.

Types of hardware:
● Motherboard
● Microprocessor
● Input devices
● Output device
● Memory device
● Secondary device
● Communication device
● Interface

# Motherboard:
● Also called as printed circuit board
● It is the main circuit board of a microcomputer
● It connect almost all of the other parts together in a computer
● Contains CPU, BIOS, memory, mass storage interface, serial/parallel
ports, expansion slots, etc

Major components of motherboard:
1. The CPU:
● Main IC chip on computer’s motherboard.
● Comes in different size and packages.
● Also known as electronic brain of computer.
● Components of CPU:
a. Arithmetic and Logic Unit (ALU)
b. Control Unit
c. Registers

Arithmetic and Logic Unit (ALU):
● Performs all the
mathematical
computation and all
comparisons in order to
make decisions.
● When CU executes
instructions related to
perform arithmetic or
logical operation on data,
it passess instruction to
ALU.

Control Unit (CU):
● Acts as central nervous
system inside the
computer for its
component.
● Also known as brain
inside a brain.
● Manages and
coordinates the entire
computer system.

Registers:
● Is a temporary storage device
which holds the data and
instructions as long as it is
being interpreted and
executed.
● When the data and
instructions are fetched from
the main memory for
processing, such data and
instructions have to be stored
in one of the registers of the
CPU.

2. The Bus:
● A set of electronic signal pathways that allows information and signals to travel
between components inside or outside of a computer is called bus.
● Electronic paths through which data travels
● Simply, the pathway which connects one chip to another or one point connected to
another point is known as a bus.
● The bus inside the system unit is termed as internal bus or system bus.
● The bus that connects external devices is termed as external bus.

Types of bus:
● Control bus
● Address bus
● Data bus

Data Bus:
● Is a line or paths for
actual flow of data to be
sent to the components.
● It carries data from the
microprocessor to
memory during the write
operation and memory to
microprocessor during
read operations.
● Can handle 64 bits which
is of 64 wires.
● The data bus moving
inside the CPU is faster
than outside the
computer.

Address Bus:
● A set of wires that
allow bits of
information with
memory addresses
for the CPU.
● The addresses in
these buses help in
locating the data in
system memory
(RAM).
● The larger the
address bus, the
better and faster will
be the performance
of the system.

Control Bus:
● Carries the necessary
timing and control
signal to manage and
coordinate the
activities of entire
computer system.
● It is used to transmit
different types of
signals such as read,
write, acknowledge,
interrupt, etc for
overall operation of
the system.

3. Expansion slots:
● They are made up of the electronic pathways that connects the
different external devices to the rest of the computer.
● These external devices ( monitor, telephone line, printer, etc) are
connected to ports on the back of the computer.
● Those ports are actually parts of a small circuit board or ‘card’ that fits
into a connector on the motherboard.
● The connector is called expansion slots.

5. CMOS battery:
● Maintains the clock function and any settings saved in CMOS storage.

6. ROM BIOS :
● ROM Basic Input Output System
● Contains a small collection of programs ( software ) which are
permanently stored on the motherboard and used when PC starts up.

# Microprocessor:
● The CPU is also called as a microprocessor
● It is the main IC chip on computer’s motherboard.
● It contains all the circuits needed to perform arithmetic logic and
control functions.
● It has a limited number of instructions that it understands is called its
instruction set.
● Each instruction involves a series of logical operations that are
performed to complete each task.

Microprocessor technologies:
● CISC technology
❖ Complex instruction set computing
❖ It combines different instructions into a single CPU, and each
instruction has the ability to perform several tasks based on mini-
programs or micro code integrated into the processor.
❖ Thus an increased number of instructions ( 200 to 300) increases the
complexity.

● RISC technology:
❖ Reduced Instruction Set Computing
❖ It takes the advantage of complexity in CISC
❖ Using several of less complex instructions together could complete the
same tasks in less time.
❖ Using fewer instruction( 128 ) requires fewer transistors, which results
in reduced manufacturing costs and a more stable, cooler operating
CPU.

Math coprocessor:
● It is a second processor in the computer that does nothing but number
crunching for the system.
● It does not perform addition, subtraction, multiplication and division of
simple numbers.
● It does calculation involving floating point (decimal) numbers, such as
scientific calculations and algebraic functions.

# Input Devices:
● Devices through which we can send the data and instruction to the computer are
known as input devices.

Some common input devices:
1. Keyboard:

3. Scanner:
● It is capable of entering information directly into the computer without
typing any information or data.
● It provides fast and more accurate data entry.
● It scans image and transforms the image to code used by the
computer.

4. Light Pen:
● It is a
photosensitive
pen lighting
device, capable
of sensing a
position on the
screen when its
tip touches the
screen.

6. Touch pad:
● It is a touch sensitive pad that is used as a pointing input device.
● We can point the objects on the screen and give commands to the
computer by putting our fingers on the touch pad.

7. Bar Code Reader:
● It is a device used for
reading bar coded data.
● Data coded in the forms of
small lines (bar) are known
as bar codes.
● A BCR uses laser-beam
scanning technology.
● Different bar codes having
different patterns of bars
reflect the beam in
different ways that is
sensed by a light sensitive
detector.

8. Optical Character Reader:
● It detects
alphanumeric
characters printed or
type written on
papers.
● The reading is done
by the light scanning
techniques in which
each character is
illuminated by a light
source and the
reflected images of
the characters are
analyzed in terms of
light and dark pattern
produced.

9. Optical Mark Reader:
● It is being used to
read answer sheet by
the means of light.
● The change in
amount of reflected
light is used to detect
the presence of mark.

10. Magnetic Ink Character Reader:
● It uses special ink to print
characters.
● It is widely used in banks
for processing cheque.
● Cheque numbers are
printed with the ink
containing magnetic
particle.

11. Digitizer:
● It is an input device used for converting pictures, maps and drawings
into digital form for storage in computer.
● Commonly used in computer aided design (CAD) by architects and
engineers to design cars, buildings, medical devices, robots, etc
● Used in geographica; information system (GIS) as well.

# Output device:
● It is an electromechanical device that accepts data from a computer
and translates them into form suitable for use by user.
● Output device generates two kinds of output:
1. Softcopy Output
2. Hardcopy Output

❖ Softcopy Output:
● The output that are temporary in nature are softcopy.
● They cannot be touched as they are not printed.
● Output given by monitor and speaker are softcopy.

1. Monitor:
● Most popular output devices.
● Similar to TV screen.
● Types of monitor:
a. Monochrome:
- information displayed in one color.
- displays text only.
b. Color Monitor:
- display output in different colors.
- types: CRT, LCD, and LED

CRT monitor:
● Cathode Ray Tude
● An electron beam is produced
by electron gun located at the
back portion of cathode ray
tube.
● The electron beam is directed
toward the front of the CRT
screen.
● A coating of phosphor material
is made on the inner surface of
the screen.
● The phosphor emits light when
it is struck by the electron
beam on the screen.

LCD monitor:
● Liquid Crystal Display
● They are thinner, lighter and
commonly used with
portable computer systems.
● They occupy less space and
power.

LED monitor:
● Light Emitting Diode
● It is advance application LCD
● Better technology than LCD
● Very accurate in color display.

❖ Hardcopy output:
● It is produced on a paper or some material that can be touched and
carried for being shown to others.
● They are permanent in nature.
● Output produced by printers and plotters are hardcopy output.

1. Printer:
● Most popular output device for hardcopy output devices.
● They provide information in a permanent readable form.
● Printers are classified based on how they print:
1. Impact printer
2. Non-impact printer

a. Impact printer:
● They use electromechanical mechanism that causes hammers or pins
strike against a ribbon and paper to print the text.
● They produce loud sound during printing.
● Also called noisy printers
● Example: Dot matrix printer, Daisy wheel printer, Drum printer, etc

Dot Matrix Printer:
● They are character
printers that print one
character at a time.
● They form characters
and all kinds of images
as a pattern of dots.
● It has a print head that
moves horizontally
(left-right and right-
left) across paper.

Drum printers:
● They are line
printers that
print an entire
line at a time.
● It consists of a
solid cylindrical
drum with
characters
embossed on
its surface in
the form of
circular bands.

b. Non-Impact printer:
● They do not use electromechanical printing mechanism.
● The use thermal, chemical, electrostatic laser beam or inkjet
technology for printing the text.
● They are faster and do not produce sound.
● Examples: Inkjet printer and laser printer

Inkjet printer:
● They are character printers
that form characters and all
kinds of images by spraying
small drops of ink on a
paper.
● They produce higher quality
printing than dot-matrix
printer.

Laser Printer:
● They are page printers
that print one page at a
time.
● Main components of laser
printers are laser beam
source, mirror,
photoconductive drum and
a toner.
● They produce a high
quality output because
they form characters by
very tiny ink particles.

Impact Printer Non-Impact Printer
It strikes an inked object i.e ribbon to form
letters.
It uses electrostatic or thermal technology
to form letter.
It produces more sound while printing. It does not produce sound while printing.
It is slower in speed. It is faster in speed.
It produces low quality output. It produces high and fine quality output.
It is cheaper in cost. It is more expensive in cost.
Example: Dot matrix printer Example: Laser printer

2. Plotters:
● They are used to produce
good quality graphics and
drawings under
computer’s control.
● They use ink pen to draw
drawings or graphics.
● A graph plotter takes as
much less time to draw
anything as compared
with traditional hand
methods of producing
drawings.

# Memory Devices:
● Memory is a piece of hardware which holds both the raw data that
needs to be processed and the results of the processing.
● Memory is a device or medium that can accept data, hold them and
deliver them on demand at a later time.
● It is the capacity of computer to store data and information.
● Types of memory:
1. Primary memory
2. Secondary memory

1. Primary memory:
● It is called main memory or internal memory.
● It is a temporary storage area built into the computer hardware.
● This memory allows CPU to store and retrieve data very quickly.
● Types of primary memory:
a. RAM
b. ROM

a. RAM
● Random access memory.
● It is also called a
temporary memory.
● RAM is a volatile
memory thus it requires
regular power supply to
hold its content.
● Types of RAM:
i. Static RAM
ii. Dynamic RAM

SRAM DRAM
Static Random Access Memory Dynamic Random Access Memory
It is made by using transistors It is made by using capacitors
It doesn’t need periodic refreshing It needs periodic refreshing
It has higher speed as compared to DRAM It has lower speed as compared to SRAM
It is more expensive It is cheaper than SRAM
It stores bit as voltage It stores bit as charge

b. ROM:
● Read only memory
● It is a computer memory on which data are pre-recorded.
● The contents on a ROM chip is written to the chip at the factory.
● Thus, it can be read, but cannot be erased or removed.
● Hence it is called non-volatile memory.
● Types of ROM:
i. Programmable ROM (PROM)
ii. Erasable Programmable ROM (EPROM)
iii. Electrically erasable PROM
iv. UV EPROM

● PROM:
- Once the program is written in it, it cannot be erased but can only be
read.
● EPROM:
- special PROM chip that can be reprogrammed to store new
information.
- the contents are stored as electrical charges and can be removed by
removing it from the circuit.
● EEPROM:
- the contents are removed by providing a certain electric current.
● UVEPROM:
- the contents are removed by exposing the chip to Ultra Violet light.

ROM RAM
It is non volatile permanent memory. It is volatile temporary memory.
It is not easily changeable. It is easily changeable.
It is mainly used to write system programs. It is mainly used to hold data for
processing.
It is useful for experts related to computer
organization.
It is useful for general user or programmer.
Data can be read only. Data can be read and write.
Its types are: PROM, EPROM, EEPROM. Its types are: SRAM , DRAM.

# Secondary Storage Devices:
● They are non-volatile memory.
● It is used to store large volume of data on permanent basis that can be
partially transferred to primary storage whenever required for
processing.
● Storage devices are classified into:
1. Sequential storage
2. Magnetic storage
3. Optical storage

1. Sequential Storage
● The device in which information can be retrieved in the same
sequence only in which it is stored.
● Here, to access the information randomly the user has to move from
the beginning to the desired file.
● Example: Magnetic Tapes.

Magnetic Tapes:
● They are capable of storing and
retaining large volumes of data.
● They were first used to record
computer data in 1951.
● Similar to tape recorder and VCR
● They are designed to store large
quantities of data approx. 26 GB
● The storage part of the tape is
commonly a ribbon that is coated with
magnetic material.
● Information is recorded in the form of
tiny non-magnetized and magnetized
spots where the presence and absence
of spots is 1 and O.

# Advantages of Magentic tape:
● Magnetic tapes are cheaper than other devices.
● Data stored on them can be erased and reused multiple times.
● They have high storage capacity
# Disadvantage:
● They tend to deteriorate over time.
● Data access is slow and a tape drive has to read the entire content

2. Magnetic Storage:
● The surface of these devices are coated with a magnetic material such
as iron oxide or ferrous oxide which can be magnetized.
● The information stored in a disk can be read many times without
affecting the stored data.
● But the writing of new data erases the data previously stored at that
location of the disk.

Some commonly used magnetic storage
devices:
# Floppy Disk :
● It is a thin plastic disk coated
with the magnetic material.
● This plastic disk is protected
by a hard outer cover.
● It is used to transfer small
amount of data.
● It has storage capacity of
1.44 MB.

# ZIP disk:
● Similar to floppy disk drives.
● It has storage capacity of 100 MB.
● Later Iomega created 250 MB and
7500 MB fo zip disk.

# Super disk:
● Similar to ZIP disk.
● It has storage capacity 120 MB
of data.
● It combined traditional magnetic
tape storage with laser heads.

# Hard Disk:
● It is the most commonly used secondary storage device.
● It is also called the magnetic disk,HDD,hard drive.
● It can store a large amount of data and information permanently.
● It contains one or more metal platters mounted on a central spindle.

Advantages of HDD:
● Large storage capacity ( 100 GB - 4 TB, so on)
● Stores and retrieves data much faster than a floppy disk or CD.
● It is fixed inside a computer so can not get mislaid.
● It is more durable and reliable than a floppy disk.
Disadvantages:
● If it fails,the computer stops working.
● Regular ‘head’ crashes can damage the surface of the disk,leading to
the loss of data.
● The disk is fixed inside the computer and cannot easily be transferred
to another computer.

# Flash Memory:
● It is more advanced type of memory available as USB memory sticks.
● Example: Pen drive, Memory cards, etc.
● Pen drive :- is most popularly used storage device also called USB
drive/thumb drive.
● Memory Card :- is small and perfect removable storage media.

3. Optical Storage Devices:
● It consists of a flat, round, portable
metal disc, which is coated with a
thin metal or plastic or other material
that is highly reflective.
● The information in optical disk is
stored in the form of pits and lands.
● The pits are the tiny reflective bumps
that are created with laser beam.
● The lands are flat areas separating
the pits.
● The land reflects the laser light,
which is read as binary digit 1.
● The pit absorbs or scatters light,
which is read as binary digit 0.

Some commonly used optical storage
devices:
# CD-ROM:
Advantages:
● It is portable
● Able to store large amount of text, images, audio and videos
● It is quite cheaper in terms of cost per character stored.
● It has a longer life span than a magnetic media.
● It is comparatively reliable and easy to use.
Disadvantages:
● It takes more time to store and retrieve data as compared to hard disk.
● It requires special drives to read/write.

# DVD-ROM:
● Digital Versatile Disk / Digital Video Disk
● Higher storage capacity than CD
● Can store data from 4.7 GB to 17 GB
# Blue Ray:
● New technology that replaces DVD
● Uses blue laser to record more data into a disc
● Can store upto 50 GB of data
● Expensive than DVD
● Most computers don’t have Blue Ray players.

# Other memories:
➔ Cache Memory:
● High speed memory.
● It stores recently used data and instructions where it can be accessed
faster.
● It is placed between CPU and Main memory.
● When CPU requires some data, it looks into the cache memory. If the
required data is present then it fetches from there.
● If the data is absent, CPU fetched data from the main memory and
stores into cache memory so that it will be easier to fetch the same
data faster if required.

# Virtual Memory:
● The process of using reserved or additional memory of secondary storage
as primary memory is known as virtual memory.
● It is a memory management technique which allows the execution of
processes that might not be completely loaded in main memory.
# Cloud Storage:
● Cloud storage is advancement in storage technology which allows storing
data online in the cloud.
● Advantages:
- Greater accessibility and reliability
- Rapid deployment
- Strong protection for data backup
- lower storage cost

# Modem:
● Modulator and Demodulator
● It is a communication device which is mainly used to transmit data
suitable for user and computer.
● It is a device by which we can connect our PC to internet service
provider over telephone line.
● The main role of modem is to convert analog signals into digital
signals and vice versa for data communication.

# Interfaces (Port):
● Ports are the connection point used to get information in and out of
the computer.
● Their arrangements may differ among computers.
● Some of the ports are colored to match a color on the device, which
will help to determine which port is used with particular device.

Some commonly used ports:
# Parallel Ports:
● They can be used to connect a
host of popular computer
peripherals like printers,
scanner, CD burner, External
hard drives, Iomega ZIP,
Network adapters, etc
● When a PC send data to a
printer using a parallel port, it
sends 8 bits of data at a time
parallelly.

# Serial Port:
● Serial ports are also called communication ports, support sequential
data transmission.
● The name “serial” comes from the fact that a serial port “serializes”
data.
● That is, it takes a byte of data and transmits the 8 bits at a time serially
one after the other.
● The main advantage is that a serial port needs only one wire to
transmit 8 bits.
● The disadvantage is that it takes 8 times longer to transmit the data.

Computer Software:
● A software is a set of programs that solve a particular problem
according to the prescribed set of instruction.
● A software instructs the computer hardware what to do.

Types of Software:
1. System Software
a. Operating System
b. Language processor
c. Utility Software
2. Application Software
a. Packaged Software
b. Tailored Software

System Software:
● System software is a special software designed to operate and
manage the internal operation of the computer system.
● They are general programs to assist the user in using application
software.
● System software supports following tasks:
- running other programs
- supports development of application software
- communicating with peripheral devices
- maintaining the use of various hardware resources such as memory,
peripherals, etc

Types of system software:
1. Operating system software:
● An operating system is a special software that controls and manages
overall operation of the computer.
● It acts as the mediator between hardware and application software.
● OSS makes a computer easier to use.
● It manages all the resources of a computer system.
● This involves performing such tasks as keeping track of who is using
what resources , granting resource request, accounting for resource
use.

2. Language Processor/Translator:
● The program or software which translates the instruction written in
human understandable language to machine language and vice versa
is called Language Processor .
● Examples: Assembler , Compiler and Interpreter

3. Utility Software:
● They are also known as service program.
● They provide service such as editing text or program, debugging
program to correct logical mistake, sorting records into particular
sequence for processing, etc.

● Some utility software are:
a. Disk defragmenter:
- it is a system tool which allows to gather the scattered data, files and
restore into a single file to increase speed.
b. Disk Clean :
- it removes unnecessary files from the computer.
c. Scan disk:
- it scan, detects and repair the disk error
d. Back up:
- it makes an extra copy of files and programs.

Application Software:
● Application softwares are the set of one or more programs designed
to carry out the operation for a specified application directly to the
users.
● It helps the user work faster, more efficiently and more productively.
● Types of application software:
a. Packaged software
b. Tailored software

a. Packaged software:
● The set of programs that allows the computer to perform the specific
data processing job for the users.
● These programs are user friendly and designed to work on more than
one environment.
● Examples: Word processing software, Spreadsheet software,
Database software, Powerpoint software, etc

b. Tailored software:
● Tailored software is the software specially designed to meet the
specific requirement of organization or individual.
● Example: Result processing software, Printing of certificates, sales
ledger, etc

System Software Application Software
They are the basic and fundamental
computer programs required for starting up
computer
They are the additional computer program
after staring up the computer
They are independent They are dependent upon system software
They communicate with user and hardware They communicate with user only
They manage files and folders They allow creating and managing
documents.
They are standard and common for every
user.
They are general and specific both.
Example: Operating system, language
processor, etc
Example: Word processing, Database,
Spreadsheet, etc

Open Source software:
● The software which are freely available in the internet and no need to
pay any amount to use them are called open source software.
● Source code of these software are freely available in internet and can
be easily downloaded.
● It has freedom to work. Everyone can modify as per their need.
● There is no restriction of law to use them.

Firmware:
● The combination of a hardware device , computer instruction and data
that reside as read only software on that device is called as Firmware.
● Firmware is simply the software that replaces the use of core
hardware.
● Firmware cannot be modified during normal operation of the device.

Computer Virus:
● Stands for Vital Information Resources Under Siege.
● A computer virus is a program that infects your computer data file.
● A virus is a small malicious computer program written in any
programming language to replicate on computers can disrupts the
normal functioning of computer.

Purpose of creating computer virus:
● To protect computer programs from piracy
● To introduce entertainment during the use of program.
● To let the software companies earn more money
● To steal private information from the server.
● To extend the programming skills.

Symptoms of Virus:
● Sometimes computer may not boot properly
● Viruses show error message on the screen
● Unwanted message, figure and picture can be seen on the screen
● It takes long time to load the program
● It changes the size of executable file
● It slows down the computer
● It reduces the memory
● It corrupts the system data
● It renames the file
● It increases the use of disk space.

Computer Antivirus:
● Antivirus are the software that can protect from viruses and eliminate
viruses so that the computer system runs smoothly.
● Antivirus performs following tasks:
a. Scans the files and folders for virus
b. Alerts the user when virus are found
c. automatically cleans the virus infected files
d. Monitors the resource of computer from virus
● Some antivirus :
- AVG, Macafee, Avast, Norton, Avira, Panda, etc

Protection from virus:
● Not to use pirated software
● Install and upgrade antivirus regularly
● Scan the mail and unknown files of internet
● Backup data regularly
● Lock the computer when not in use
● Use the password to avoid unauthorized access

Chapter 5. computer system

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