Textbook: Inside Computers- Hardware and Operating Systems | Computer Science for Class 7 PDF Download

 Page 1


Aim: In this lesson, you will learn:
- The main hardware and software components of a computer.
- Functions of different computer parts.        
Inside Computers: Hardware and 
Operating Systems 2
Tejas, Jyoti and their 
friends along with Moz are 
examining an open CPU 
(Central Processing Unit).
Jyoti: Computers are 
made of electronic parts 
called components. Each 
component has a specific 
function. They all work 
together when a computer 
is operated. Some of the 
components can be seen 
partly from the outside. 
Some components are 
inside the computer box where we can’t see them.
Tejas: Seeing the components inside a computer is interesting. Look at the brain of the computer 
(CPU). Whenever we press a key, click the mouse, or start an application, we send instructions to 
the CPU. These are all executed by the CPU.
Jyoti: Look at these other components. How can we know their details?
Moz: We can do by starting the computer and exploring the system. The lesson contains description 
of each of the parts 1 to 9 labelled in the figure below. Lets go to the lab now.
Tejas, Jyoti and Moz move to the computer lab discussing about the components of a computer.
Jyoti: Can we see the details of a computer’s components after logging in?
Moz: Yes. On the desktop, from the taskbar, click on the System sub-menu. Under 
Administration click on System Monitor, which shows you details and status of hardware and  
software of the computer.
 8.Monitor
Keyboard
  3.Hard Disk
Mouse
 6.Power Supply
 1.Processor
 2.Main Memory
 9.BIOS
 7.Mother Board
4
Page 2


Aim: In this lesson, you will learn:
- The main hardware and software components of a computer.
- Functions of different computer parts.        
Inside Computers: Hardware and 
Operating Systems 2
Tejas, Jyoti and their 
friends along with Moz are 
examining an open CPU 
(Central Processing Unit).
Jyoti: Computers are 
made of electronic parts 
called components. Each 
component has a specific 
function. They all work 
together when a computer 
is operated. Some of the 
components can be seen 
partly from the outside. 
Some components are 
inside the computer box where we can’t see them.
Tejas: Seeing the components inside a computer is interesting. Look at the brain of the computer 
(CPU). Whenever we press a key, click the mouse, or start an application, we send instructions to 
the CPU. These are all executed by the CPU.
Jyoti: Look at these other components. How can we know their details?
Moz: We can do by starting the computer and exploring the system. The lesson contains description 
of each of the parts 1 to 9 labelled in the figure below. Lets go to the lab now.
Tejas, Jyoti and Moz move to the computer lab discussing about the components of a computer.
Jyoti: Can we see the details of a computer’s components after logging in?
Moz: Yes. On the desktop, from the taskbar, click on the System sub-menu. Under 
Administration click on System Monitor, which shows you details and status of hardware and  
software of the computer.
 8.Monitor
Keyboard
  3.Hard Disk
Mouse
 6.Power Supply
 1.Processor
 2.Main Memory
 9.BIOS
 7.Mother Board
4
Jyoti: Hey! There are four processors (CPU) in this computer. There are many details 
for the processors. 
Moz: The processing of your instructions is shared between the four processors, just the way you 
share work among your team. 
Jyoti:  What does  2.66 GHz  mean?
Moz: This stands for 2.66 Giga Hertz. You know that Mega means million and Giga means 
billion. Hertz  is a unit of measurment that measures the processing speed. It means cycles per 
second. CPU needs one or  more cycles to perform an action. More cycles per seconds means that 
the CPU can process more instructions per second. So, the higher the processing speed, the faster 
the CPU can process instructions.
Central 
Processing Unit
(CPU)
Executes program 
commands
Processor (CPU)
1 1
Processor (CPU)
The Central Processing Unit (CPU), also called 
a processor, is like the brain of the computer. It 
executes instructions in response to commands.
A processor’s speed is measured in •	 Megahertz 
(MHZ), or Gigahertz (GHZ). Higher the speed, 
faster is the execution of instructions. 
The CPU is generally a •	 2 inch ceramic square 
with a silicon chip located inside. The chip is 
usually about the size of a thumbnail. 
Info Concept
Page 3


Aim: In this lesson, you will learn:
- The main hardware and software components of a computer.
- Functions of different computer parts.        
Inside Computers: Hardware and 
Operating Systems 2
Tejas, Jyoti and their 
friends along with Moz are 
examining an open CPU 
(Central Processing Unit).
Jyoti: Computers are 
made of electronic parts 
called components. Each 
component has a specific 
function. They all work 
together when a computer 
is operated. Some of the 
components can be seen 
partly from the outside. 
Some components are 
inside the computer box where we can’t see them.
Tejas: Seeing the components inside a computer is interesting. Look at the brain of the computer 
(CPU). Whenever we press a key, click the mouse, or start an application, we send instructions to 
the CPU. These are all executed by the CPU.
Jyoti: Look at these other components. How can we know their details?
Moz: We can do by starting the computer and exploring the system. The lesson contains description 
of each of the parts 1 to 9 labelled in the figure below. Lets go to the lab now.
Tejas, Jyoti and Moz move to the computer lab discussing about the components of a computer.
Jyoti: Can we see the details of a computer’s components after logging in?
Moz: Yes. On the desktop, from the taskbar, click on the System sub-menu. Under 
Administration click on System Monitor, which shows you details and status of hardware and  
software of the computer.
 8.Monitor
Keyboard
  3.Hard Disk
Mouse
 6.Power Supply
 1.Processor
 2.Main Memory
 9.BIOS
 7.Mother Board
4
Jyoti: Hey! There are four processors (CPU) in this computer. There are many details 
for the processors. 
Moz: The processing of your instructions is shared between the four processors, just the way you 
share work among your team. 
Jyoti:  What does  2.66 GHz  mean?
Moz: This stands for 2.66 Giga Hertz. You know that Mega means million and Giga means 
billion. Hertz  is a unit of measurment that measures the processing speed. It means cycles per 
second. CPU needs one or  more cycles to perform an action. More cycles per seconds means that 
the CPU can process more instructions per second. So, the higher the processing speed, the faster 
the CPU can process instructions.
Central 
Processing Unit
(CPU)
Executes program 
commands
Processor (CPU)
1 1
Processor (CPU)
The Central Processing Unit (CPU), also called 
a processor, is like the brain of the computer. It 
executes instructions in response to commands.
A processor’s speed is measured in •	 Megahertz 
(MHZ), or Gigahertz (GHZ). Higher the speed, 
faster is the execution of instructions. 
The CPU is generally a •	 2 inch ceramic square 
with a silicon chip located inside. The chip is 
usually about the size of a thumbnail. 
Info Concept
Tejas: Main memory is used to store programs and data that are currently processed.. 
Moz: The computer’s instructions are stored in Random Access Memory (RAM). This is where 
programs executes. For example, when you using word processor application to create a document 
or Scratch to create an animation, the corresponding instructions are loaded into the RAM.
Jyoti: What does 3.2 GiB mean?  
Moz: Let us first understand how computers store information. Computers store information as 
numbers, in a binary system. A binary system has only two numbers 0 and 1. (Decimal system 
has 10 numbers 0.....9.)
Processor (CPU)
1 2
Main Memory (Primary)
Primary storage area 
for programs and data 
that are in active use
Main 
Memory
Central 
Processing Unit
(CPU)
Executes program 
commands
Info Concept
RAM (Random Access Memory) is  also called main memory. RAM is •	
used  to store data and instructions that are currently being processed by  
 a computer’s CPU. 
Data  is temporarily stored in the RAM till it is saved  to the hard disk. The data •	
in RAM is erased when power is switched off.
RAM is measured in •	 megabytes (MB) or gigabytes (GB). A bit is the smallest 
unit of data in computer processing. It represents a digit in the binary system. 
So a bit can have either a value 0 or value 1. 
A byte is a group of eight bits. •	
 Example of Bit :            or
                    Byte:  
A •	 Kilobyte (KB) is 2
10
 bytes or 1024 bytes. A Megabyte (MB) is 1024 kilobytes. 
A gigabyte (GB) is 1,024 megabytes. 
The •	 more RAM a computer has, the more data it a can access quickly. So 
more the RAM, the faster a computer performs tasks.
Ubuntu OS by default uses Gibibyte or GiB to denote its memory, while •	
Windows uses Gigabyte or GB by default.
Though GiB is closely related to GB, the actual conversion is 1 GiB (nearly •	
equals to sign) ~ 1.074 GB
1 0 1 0 1 1 0 1
0 1
RAM
Page 4


Aim: In this lesson, you will learn:
- The main hardware and software components of a computer.
- Functions of different computer parts.        
Inside Computers: Hardware and 
Operating Systems 2
Tejas, Jyoti and their 
friends along with Moz are 
examining an open CPU 
(Central Processing Unit).
Jyoti: Computers are 
made of electronic parts 
called components. Each 
component has a specific 
function. They all work 
together when a computer 
is operated. Some of the 
components can be seen 
partly from the outside. 
Some components are 
inside the computer box where we can’t see them.
Tejas: Seeing the components inside a computer is interesting. Look at the brain of the computer 
(CPU). Whenever we press a key, click the mouse, or start an application, we send instructions to 
the CPU. These are all executed by the CPU.
Jyoti: Look at these other components. How can we know their details?
Moz: We can do by starting the computer and exploring the system. The lesson contains description 
of each of the parts 1 to 9 labelled in the figure below. Lets go to the lab now.
Tejas, Jyoti and Moz move to the computer lab discussing about the components of a computer.
Jyoti: Can we see the details of a computer’s components after logging in?
Moz: Yes. On the desktop, from the taskbar, click on the System sub-menu. Under 
Administration click on System Monitor, which shows you details and status of hardware and  
software of the computer.
 8.Monitor
Keyboard
  3.Hard Disk
Mouse
 6.Power Supply
 1.Processor
 2.Main Memory
 9.BIOS
 7.Mother Board
4
Jyoti: Hey! There are four processors (CPU) in this computer. There are many details 
for the processors. 
Moz: The processing of your instructions is shared between the four processors, just the way you 
share work among your team. 
Jyoti:  What does  2.66 GHz  mean?
Moz: This stands for 2.66 Giga Hertz. You know that Mega means million and Giga means 
billion. Hertz  is a unit of measurment that measures the processing speed. It means cycles per 
second. CPU needs one or  more cycles to perform an action. More cycles per seconds means that 
the CPU can process more instructions per second. So, the higher the processing speed, the faster 
the CPU can process instructions.
Central 
Processing Unit
(CPU)
Executes program 
commands
Processor (CPU)
1 1
Processor (CPU)
The Central Processing Unit (CPU), also called 
a processor, is like the brain of the computer. It 
executes instructions in response to commands.
A processor’s speed is measured in •	 Megahertz 
(MHZ), or Gigahertz (GHZ). Higher the speed, 
faster is the execution of instructions. 
The CPU is generally a •	 2 inch ceramic square 
with a silicon chip located inside. The chip is 
usually about the size of a thumbnail. 
Info Concept
Tejas: Main memory is used to store programs and data that are currently processed.. 
Moz: The computer’s instructions are stored in Random Access Memory (RAM). This is where 
programs executes. For example, when you using word processor application to create a document 
or Scratch to create an animation, the corresponding instructions are loaded into the RAM.
Jyoti: What does 3.2 GiB mean?  
Moz: Let us first understand how computers store information. Computers store information as 
numbers, in a binary system. A binary system has only two numbers 0 and 1. (Decimal system 
has 10 numbers 0.....9.)
Processor (CPU)
1 2
Main Memory (Primary)
Primary storage area 
for programs and data 
that are in active use
Main 
Memory
Central 
Processing Unit
(CPU)
Executes program 
commands
Info Concept
RAM (Random Access Memory) is  also called main memory. RAM is •	
used  to store data and instructions that are currently being processed by  
 a computer’s CPU. 
Data  is temporarily stored in the RAM till it is saved  to the hard disk. The data •	
in RAM is erased when power is switched off.
RAM is measured in •	 megabytes (MB) or gigabytes (GB). A bit is the smallest 
unit of data in computer processing. It represents a digit in the binary system. 
So a bit can have either a value 0 or value 1. 
A byte is a group of eight bits. •	
 Example of Bit :            or
                    Byte:  
A •	 Kilobyte (KB) is 2
10
 bytes or 1024 bytes. A Megabyte (MB) is 1024 kilobytes. 
A gigabyte (GB) is 1,024 megabytes. 
The •	 more RAM a computer has, the more data it a can access quickly. So 
more the RAM, the faster a computer performs tasks.
Ubuntu OS by default uses Gibibyte or GiB to denote its memory, while •	
Windows uses Gigabyte or GB by default.
Though GiB is closely related to GB, the actual conversion is 1 GiB (nearly •	
equals to sign) ~ 1.074 GB
1 0 1 0 1 1 0 1
0 1
RAM
Moz: The hard disk stores multiple types of data and applications. The documents and content 
that a user creates and saves, the software to operate the computer, and the applications like Word 
processor and Scratch, are stored on the hard disk. The computer loads the instructions from 
secondary memory (hard disk) into main memory (RAM) as and when required. 
Jyoti: The amount of data and the numbers of programs that we can store on a hard disk depends 
on the size of the disk, which is usually measured in giga bytes (GB). 
Jyoti: When we save data in an application, the content is written into secondary memory.
Tejas: Whatever information we save on a computer, is written to the hard disk, which can be 
retrieved later. It is a permanent storage device. 
Processor (CPU)
1 3
Secondary memory (Hard disk and removable storage)
Central 
Processing Unit
(CPU)
Information is moved between 
main memory and secondary 
memory as needed.
Hard disk
CD/DVD
Pendrive
Main 
Memory
Tejas: We can also record data to CD/DVD or pen drive. The storage capacity of these devices is 
usually not as much as a hard disk drive.
Moz: Correct. These devices are called removable storage devices. These can be removed from 
the computer and carried wherever required. (The hard disk is also sometimes removable.)
Jyoti: A few days ago I created a greeting using the computer. I saved it on the hard disk and also 
copied it on to a pen drive. Next day, the computer did not work. But since I had a copy on the 
pen drive, I could copy the file on to another computer and mail it to my friends.
Info Concept
Secondary storage is the memory where the information is •	
stored permanently, till it is explicitly deleted. Information 
is moved between main memory and secondary memory 
as and when needed. 
On power off of a computer, data on hard disk and other •	
secondary storage devices are not erased. 
The hard disk drive is the data center of the computer. 1. 
Operating system, software, content (created and saved 
by users) are stored here until explicitly deleted. The hard 
disk drive is usually found inside a computer. 
CD/DVD and pen drive are removable storage devices. 2. 
These can be used to backup important data and 
information. They also are used to distribute, share 
information or transfer information from one computer  
to another.
CD/DVD
2
Pen drive
1 Hard disk
Page 5


Aim: In this lesson, you will learn:
- The main hardware and software components of a computer.
- Functions of different computer parts.        
Inside Computers: Hardware and 
Operating Systems 2
Tejas, Jyoti and their 
friends along with Moz are 
examining an open CPU 
(Central Processing Unit).
Jyoti: Computers are 
made of electronic parts 
called components. Each 
component has a specific 
function. They all work 
together when a computer 
is operated. Some of the 
components can be seen 
partly from the outside. 
Some components are 
inside the computer box where we can’t see them.
Tejas: Seeing the components inside a computer is interesting. Look at the brain of the computer 
(CPU). Whenever we press a key, click the mouse, or start an application, we send instructions to 
the CPU. These are all executed by the CPU.
Jyoti: Look at these other components. How can we know their details?
Moz: We can do by starting the computer and exploring the system. The lesson contains description 
of each of the parts 1 to 9 labelled in the figure below. Lets go to the lab now.
Tejas, Jyoti and Moz move to the computer lab discussing about the components of a computer.
Jyoti: Can we see the details of a computer’s components after logging in?
Moz: Yes. On the desktop, from the taskbar, click on the System sub-menu. Under 
Administration click on System Monitor, which shows you details and status of hardware and  
software of the computer.
 8.Monitor
Keyboard
  3.Hard Disk
Mouse
 6.Power Supply
 1.Processor
 2.Main Memory
 9.BIOS
 7.Mother Board
4
Jyoti: Hey! There are four processors (CPU) in this computer. There are many details 
for the processors. 
Moz: The processing of your instructions is shared between the four processors, just the way you 
share work among your team. 
Jyoti:  What does  2.66 GHz  mean?
Moz: This stands for 2.66 Giga Hertz. You know that Mega means million and Giga means 
billion. Hertz  is a unit of measurment that measures the processing speed. It means cycles per 
second. CPU needs one or  more cycles to perform an action. More cycles per seconds means that 
the CPU can process more instructions per second. So, the higher the processing speed, the faster 
the CPU can process instructions.
Central 
Processing Unit
(CPU)
Executes program 
commands
Processor (CPU)
1 1
Processor (CPU)
The Central Processing Unit (CPU), also called 
a processor, is like the brain of the computer. It 
executes instructions in response to commands.
A processor’s speed is measured in •	 Megahertz 
(MHZ), or Gigahertz (GHZ). Higher the speed, 
faster is the execution of instructions. 
The CPU is generally a •	 2 inch ceramic square 
with a silicon chip located inside. The chip is 
usually about the size of a thumbnail. 
Info Concept
Tejas: Main memory is used to store programs and data that are currently processed.. 
Moz: The computer’s instructions are stored in Random Access Memory (RAM). This is where 
programs executes. For example, when you using word processor application to create a document 
or Scratch to create an animation, the corresponding instructions are loaded into the RAM.
Jyoti: What does 3.2 GiB mean?  
Moz: Let us first understand how computers store information. Computers store information as 
numbers, in a binary system. A binary system has only two numbers 0 and 1. (Decimal system 
has 10 numbers 0.....9.)
Processor (CPU)
1 2
Main Memory (Primary)
Primary storage area 
for programs and data 
that are in active use
Main 
Memory
Central 
Processing Unit
(CPU)
Executes program 
commands
Info Concept
RAM (Random Access Memory) is  also called main memory. RAM is •	
used  to store data and instructions that are currently being processed by  
 a computer’s CPU. 
Data  is temporarily stored in the RAM till it is saved  to the hard disk. The data •	
in RAM is erased when power is switched off.
RAM is measured in •	 megabytes (MB) or gigabytes (GB). A bit is the smallest 
unit of data in computer processing. It represents a digit in the binary system. 
So a bit can have either a value 0 or value 1. 
A byte is a group of eight bits. •	
 Example of Bit :            or
                    Byte:  
A •	 Kilobyte (KB) is 2
10
 bytes or 1024 bytes. A Megabyte (MB) is 1024 kilobytes. 
A gigabyte (GB) is 1,024 megabytes. 
The •	 more RAM a computer has, the more data it a can access quickly. So 
more the RAM, the faster a computer performs tasks.
Ubuntu OS by default uses Gibibyte or GiB to denote its memory, while •	
Windows uses Gigabyte or GB by default.
Though GiB is closely related to GB, the actual conversion is 1 GiB (nearly •	
equals to sign) ~ 1.074 GB
1 0 1 0 1 1 0 1
0 1
RAM
Moz: The hard disk stores multiple types of data and applications. The documents and content 
that a user creates and saves, the software to operate the computer, and the applications like Word 
processor and Scratch, are stored on the hard disk. The computer loads the instructions from 
secondary memory (hard disk) into main memory (RAM) as and when required. 
Jyoti: The amount of data and the numbers of programs that we can store on a hard disk depends 
on the size of the disk, which is usually measured in giga bytes (GB). 
Jyoti: When we save data in an application, the content is written into secondary memory.
Tejas: Whatever information we save on a computer, is written to the hard disk, which can be 
retrieved later. It is a permanent storage device. 
Processor (CPU)
1 3
Secondary memory (Hard disk and removable storage)
Central 
Processing Unit
(CPU)
Information is moved between 
main memory and secondary 
memory as needed.
Hard disk
CD/DVD
Pendrive
Main 
Memory
Tejas: We can also record data to CD/DVD or pen drive. The storage capacity of these devices is 
usually not as much as a hard disk drive.
Moz: Correct. These devices are called removable storage devices. These can be removed from 
the computer and carried wherever required. (The hard disk is also sometimes removable.)
Jyoti: A few days ago I created a greeting using the computer. I saved it on the hard disk and also 
copied it on to a pen drive. Next day, the computer did not work. But since I had a copy on the 
pen drive, I could copy the file on to another computer and mail it to my friends.
Info Concept
Secondary storage is the memory where the information is •	
stored permanently, till it is explicitly deleted. Information 
is moved between main memory and secondary memory 
as and when needed. 
On power off of a computer, data on hard disk and other •	
secondary storage devices are not erased. 
The hard disk drive is the data center of the computer. 1. 
Operating system, software, content (created and saved 
by users) are stored here until explicitly deleted. The hard 
disk drive is usually found inside a computer. 
CD/DVD and pen drive are removable storage devices. 2. 
These can be used to backup important data and 
information. They also are used to distribute, share 
information or transfer information from one computer  
to another.
CD/DVD
2
Pen drive
1 Hard disk
Jyoti: We already 
know what are input 
and output devices.      
   Examples of input 
devices are keyboard, 
digital camera, and 
mouse. Printer and 
Monitor are examples 
of output devices.
Moz: Correct. User 
interacts with the computer using these devices. These are also called peripheral devices. The 
electrical signals for the alphabets typed on a keyboard are converted to binary system and stored. 
When the computer displays the data on a monitor or when data is to be printed, the binary 
system is again converted to electrical signals and then to the human understandable characters.
Tejas: Oh! This is how input gets converted to output in a computer.
Info Concept
An input device converts data and instructions entered using the •	
device into a pattern of electrical signals. These signals correspond 
to binary code that can be processed by a digital computer. A user 
inputs data and instructions (example: using a keyboard), initiates 
a task (example: using a mouse), transfers images (example: using 
a web camera), using the input devices.
An output device reverses the process, translating the binary •	
code into a form intelligible to the user. The computer displays  
processed information (example: a print out of the information or 
audio, video) through the output devices.
Some devices can handle both input and output. The network •	
device (called network card) in a computer is both input and  
output device.
Keyboard
Scanner
Mouse
Processor (CPU)
1 4
Input/Output (I/O) devices
Input devices are used to send information to the computer and output devices are used to receive information from the computer. CPU is 
neither an input nor an output device. It takes information from the input devices, processes it and sends the result to the output devices. This 
is called processing.
Moz: Making a copy of a document or information that you create on the computer, is called taking 
backup. Backup of content (documents, paintings, reports, etc.) that you create is important. 
Backup can be taken on CD/DVD, pendrive, a removable hard disk, or another computer to 
which you have access.
Tejas: We can also mail a copy to ourselves if we have Internet connectivity. 
Moz: Right. This is good option when you have Internet connectivity.
Jyoti: We also get books, games, educational lessons on CD/DVDs. 
Moz: Correct. These devices can also be used for distribution and sharing of resources.
Making a copy of data is called Backup. Backup of data and information that you create is 
important. Many backup options are available, like mailing a copy of the content to yourself, 
taking a backup on pen drive, a CD/DVD or another computer. This ensures that even if 
one device fails, you have a copy of the content and can access it using another computer. 
Backup
Concept
Electrical
Electrical
Signals
Signals
1 0 1 0 1 1 0 1
Keyboard
‘A’ Pressed
Monitor
‘A’ Displayed
CPU and Memory
1 0 1 0 1 1 0 1
1
1
11