The document serves as an introduction to computer systems, covering critical components such as hardware and software, the central processing unit (CPU), memory types (RAM, ROM, and cache), and storage devices. It explains how these elements interact and highlights commonly used computer terms. The content is aimed at providing foundational knowledge of computer organization and functionality.

1. INTRODUCTION TO COMPUTERS
Mukesh N. Tekwani
2019
Email: mukeshnt@yahoo.com
B. Voc. – Computer Skills Course
Prof Mukesh N Tekwani, 2019 1

2. Session 2 Objectives:
1. Various Parts of a Computer
2. Peripheral Devices
3. Commonly Used Computer Terms
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3. Various Parts of a Computer
1. Hardware
a) Physical parts
b) Can be touched and felt.
2. Software
a) Programs or instructions given to
hardware
b) Cannot be touched / feltProf Mukesh N Tekwani, 2019 3

4. Various Parts of a Computer
1. Hardware
a) TV set, mobile phone
b) Computer / laptop
2. Software
a) Programmes we watch on TV
b) Programmes we run on computers or
mobile phoneProf Mukesh N Tekwani, 2019 4

5. Various Parts of a Computer
1. Hardware and software cannot work
independently of each other.
2. You may have a TV but without
programmes, no fun !
3. Programmes may be telecast, but if you
have no hardware (TV/set-top box), no fun!Prof Mukesh N Tekwani, 2019 5

6. Various Parts of a Computer
1. Hardware is the electronic circuits of a
computer.
2. Various components and devices like hard
disk, monitor, mouse, keyboard….
3. Every computer :
1. Central Processing Unit + Secondary
Storage Devices + Peripheral Devices
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7. Various Parts of a Computer
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8. Block Diagram of a Computer
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9. The CPU
CPU is the brain of a computer.
All tasks such as calculations, decision-making, controlling other
devices carried out by the CPU
Parts of A CPU:
1. Control Unit
2. ALU – Arithmetic and Logic Unit
3. Registers
4. Cache memory
5. Primary & Temporary Memory RAM- Random Access Memory
6. Primary & Permanent Memory ROM-Read Only Memory
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10. Control Unit (C.U.)
1. Manage resources of a computer.
2. Controls the working of the entire computer system.
3. Contains the firmware – i.e. instructions for execution of
programs
4. Stores all operations that can be carried out by a computer
5. This list of operations that a CU can perform is called its
Instruction Set.
6. The CU directs the flow of data around the CPU and around
the computer
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11. Arithmetic and Logic Unit (ALU)
1. All arithmetic operations like +, -, x and /
2. Logic operations such as comparison like <, <=, >, >= , AND, .
3. Registers are included in the ALU. They work under the
directions of the CU. These registers store the data that is
being processed.
4. Registers are like memory cells but have high speed (~1 ns)
5. Registers can store data or instructions – so there are 2 types
of registers – Data Register and Instruction Register
6. Registers are the smallest, high-speed storage area in the
CPU.
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12. Primary Memory
1. Consists of RAM and ROM
2. RAM – Random Access Memory (Temporary)
3. ROM – Read Only Memory (Permanent)
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13. Random Access Memory (RAM)
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14. Random Access Memory (RAM)
1. Before the CPU can process any information, it must be
stored in the RAM.
2. All inputs from the keyboard, mouse, etc first go into the
RAM before the CPU can process them
3. RAM is called as a primary memory. Before the data can be
saved to a disk/USB drive / CD, etc, it must be in RAM
4. RAM is a temporary memory. It can store data only as long as
power is supplied to the computer. Power Off  Data in RAM
is lost. Hence, RAM is also called Volatile memory
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15. Random Access Memory (RAM)
5. RAM is available in various sizes – 4 GB, 8 GB, etc.
6. More RAM may mean the computer will work faster – but not
always.
7. RAM has a speed measured in mega hertz (MHz). More the
speed, faster is the data transfer to and from RAM.
8. Why is it called Random Access Memory? ANY location in this
memory can be accessed with the same speed (unlike a tape)
9. We can increase RAM in a computer but upto a certain limit.
10. Typical speed is 1 ns (10-9 s)Prof Mukesh N Tekwani, 2019 15

16. Types of RAM
1. Dynamic RAM (DRAM) - This memory must be constantly
refreshed or reenergised otherwise all contents are lost.
Cheaper comparatively.
2. Static RAM (SRAM) – faster, requires less power but is more
expensive. Need not be refreshed like DRAM.
3. Synchronous Dynamic RAM (SDRAM) – This can run at very
high clock speeds. This is the most common primary memory
now. DDR5, DDR4, DDR3, etc are different versions of SDRAM.
4. DDR – Double Data Rate Synchronous Random Access MmeoryProf Mukesh N Tekwani, 2019 16

17. Read Only Memory (ROM)
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18. Read Only Memory (ROM)
1. ROM is built onto the motherboard
2. Data and instructions stored in ROM cannot be changed by
user.
3. User can READ the data and instructions in ROM but cannot
modify it.
4. Why does a computer need ROM ? When a computer is
switched on it must perform certain tasks on its own. These
instructions are stored in the ROM.
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19. Read Only Memory (ROM)
5. Instructions stored in the ROM are – search for devices
connected to the computer, search for keyboard, mouse,
check the RAM, etc. This process is called the BOOTUP
process.
6. The ROM also looks for the Operating System (Windows) on
the hard disk.
7. This memory is NOT LOST when power is switched off. Hence
it is called permanent or non-volatile memory.
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20. Types of ROM
1. Programmable ROM – Programmable Read Only Memory. Store
instructions once only.
2. Erasable Programmable Read Only Memory (EPROM) – store
instructions but they can be erased only by exposing the
memory to ultraviolet light
3. Electrically Erasable Programmable Read Only Memory
(EEPROM) – store and delete instructions on a special circuit
boardProf Mukesh N Tekwani, 2019 20

21. Cache Memory
1. This is a type of memory that keeps copies of frequently used
data.
2. Cache supplies data to the registers whenever CPU wants to
perform some calculation.
3. Cache is much faster than RAM (typical access time is 5 ns)
4. Cache is physically closer to the processor.
5. CPU will first check for data in the cache before it searches
for the same data in RAM.
6. Hard disk and CD-ROM also have their own cache memoryProf Mukesh N Tekwani, 2019 21

22. Secondary Storage (Permanent Storage)
1. Data and programs (software) must be saved permanently so
that they can be used again.
2. This permanent storage is the hard disk.
3. Other permanent storage devices are : USB/pen drive,
CDROM, DVDROM, magnetic tape, solid state disk
4. Hard disk, magnetic tape are sensitive to magnetic fields –
keep away from strong magnets, TV sets, powerful speakers.
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23. 1. This is a permanent storage.
2. Data and programs are stored on magnetic disks.
3. Various spots on this disk can be magnetised.
4. Each magnetised & unmagnetized spot represents a binary 1
or 0
5. The metal platters spin on a spindle and the entire unit is
kept in a sealed chamber
6. Typical capacity is about 1 TB (terra byte) (10^12 bytes)
7. There are READ/WRITE heads that can magnetise a spot
(WRITE) or read the data (detect a magnetised spot)
Hard Disk
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24. Hard Disk
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25. Parts of a Hard Disk
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26. Optical Disks
1. Optical disks use a laser beam to store data on a plastic substance called
Compact Disk (CD) and the same laser beam can also read the data on the disk
2. Very large amount of data can be stored on optical disks
3. Optical disks are ideally suited for storing video, audio, games, distributing
applications
4. There are two types of CD-ROM: (i) write-once and (ii) re-writeable
5. CD-ROM – has a capacity of about 700 MB
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27. Pros and Cons of CD-ROM
Advantages of CD-ROM:
a. It is a very cheap medium of data storage. A 700 MB CD-ROM will cost around
Rs 10 – 20
b. CD-ROM is durable and data can be stored for a very long time.
c. Data is not affected by magnetic fields
Disadvantages of CD-ROM:
a. Once data is stored, it cannot be edited on the same disk.
b. Data storage and retrieval is a slow process compared to hard disk
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28. Optical Disks
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29. Digital Video Disk (DVD)
1. DVD is similar to a CD-ROM.
2. It uses a laser beam to write and read data
3. Data is stored in pits and lands
4. It has a greater storage capacity compared to a CD-ROM
5. DVD can store upto 17 GB of data
6. DVD can store data once (DVD-R)
7. DVD-RW can store data many times
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30. Optical Disks
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31. Hierarchy of Memory
REGISTERS
LEVEL 1 CACHE
MEMORY
LEVEL 2 CACHE MEMORY
MAIN MEMORY (RAM)
LOCAL SECONDARY STORAGE
(HARD DISK, CD-ROM, SOLOID-STATE DEVICES)
REMOTE SECONADRY STORAGE (WEB SERVERS)
Smaller
Faster
Costlier
Larger
Slower
Cheaper
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32. Comparison of various Storage Devices
Storage Speed Capacity Cost Permanent ?
Registers Fastest Lowest Highest No
RAM Very fast Low/Moderate High No
ROM Very fast Very Low High Yes
Hard Disk Moderate Very High Very Low Yes
CD-ROM Moderate High Very Low Yes
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33. Commonly Used Computer Terms
1. ABORT – To stop or terminate a program before it has finished. (program ‘hangs’ –
computer cannot be used)
2. ALGORITHM – set of instructions to solve a problem (like a cookbook recipe)
3. ANTIVIRUS PROGRAM – A utility 9or software) that searches the hard disk for any
virus and removes it
4. VIRUS – Any unwanted program that causes damage to software or data or
communication system
5. BANDWIDTH – The amount of data that can be transmitted in a given amount of
time. It is measured in bytes per sec (Bps) or bits per sec (bps) – give example
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34. Commonly Used Computer Terms
6. BIT – smallest unit of information. Abbreviation of Binary Digit. It can be a 0 or a 1.
7. BYTE – a group of 8 bits is called a Byte. Each character requires 1 byte of storage
8. BOOT – the process of starting a computer. The BOOT program is stored in the
computer’s ROM
9. CACHE – An area of memory where frequently used data is stored so that it can be
given to the CPU quickly
10.CHARACTER – A number, alphabet, or symbol is called a character (‘A’, ‘+’, 5, etc)
11.COMPATIBLE – The ability of one hardware or software to work with another
hardware or software.
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35. Commonly Used Computer Terms
12.ICON – A graphical element on the screen which executes a program when it is
selected and clicked
13.MOTHER BOARD – The main circuit board in a computer which has the processor,
RAM, cache, ROM and which carries electrical signals and data from one part of
computer to another
14.NUMERIC KEYPAD – This is usually found on the right side of a keyboard and
contains keys for entering numeric data, keys for +, -, * and / and arrow keys for
navigation. Useful for fast data entry.
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