Computer Organization Class 11 Notes | IT 802 Unit-1

IT 802 Unit 1 Computer Organization Class 11 Notes designed as per CBSE suggested syllabus covering all topics in easy language and concisely. This Computer Organization Class 11 Notes is very useful and specially designed by well experienced IT professional for all those students learning IT 802 Class 11.

Session 1: Fundamentals of Computer

What is Computer System

a computer as a machine which executes a set of instructions provided by the user to produce the desired output. As per Oxford Dictionary, a computer is defined as “an electronic device which is capable of receiving information (data) in a particular form and of performing a sequence of operations in accordance with a predetermined but variable set of procedural instructions (program) to produce a result in the form of information or signals.”.

Characteristics of a Computer

Computer has become an inseparable part of our lives today because of following characteristics:

Characteristics of Computer Computer Organization Class 11 Notes

Speed: Computer has the ability to process data and instructions at a very high speed. A typical high-speed computer can perform about 3-4 MIPS (Million Instructions Per Second).

Versatility: is the ability of a computer to do a variety of jobs with ease. You can use Computer System for any kind of work like calculations, documentation, presentations, games, database management, communication etc.

Accuracy: The term Accuracy is related to output produced by Computer System is always correct and precise. If any error occurs is not produced by Computers but by humans.

Diligence: It is the ability to perform the same task repeatedly over and over again without losing efficiency and accuracy.

Memory: It is one of the most valuable features of a computer. It is actually ability to store data either temporarily or permanently in computer.

Intelligence: earlier days of computers did not have the ability to take decisions of their own because they were just programmed to perform certain tasks. But now a days, with the advent of artificial intelligence techniques, computer can also take decisions self and reprogrammed itself to meet the desired result.

Components of a Computer

The computer is the combination of hardware and software. Hardware is the tangible parts of a computer that you can see or touch like mouse, monitor, keyboard etc. while software is the set of programs or instructions that instruct hardware to perform a task. Hence both software and hardware make the computer system function.

Let us discuss each component and its functionality:

Input Devices

devices used for input like mouse, keyboard, scanner, microphone are called input device.

Storage Devices

There are basically two types of computer storage devices:

Primary Memory

Data stored in Primary Memory is directly accessible by the CPU and it is relatively fast and expensive as compared to the secondary storage. It is also called main memory, or working memory of the machine. Primary memory is of two types:

RAM (Random Access Memory)

It is a primary volatile memory i.e. its data gets lost once the power supply is stopped. RAM is of two types: DRAM (Dynamic Random Access Memory) and SRAM ( Static Random Access Memory).

Used in main memoryIt is used in cache
 Uses less power Use more power
slower than SRAMFaster than DRAM

ROM (Read Only Memory)

It is generally used in startup operations of computer. It is a non-volatile primary memory. Further it may be classified as : ROM, PROM(Programmable read only memory), EPROM ( Erasable Programmable read only memory), EEPROM ( Electrically Erasable Programmable read only memory)

Secondary Storage

The memory which is external to the computer system and stores data permanently forms the secondary storage like hard disk, CD, DVD, pen drives etc.

Cache Memory

It is a very high speed memory which is used to further enhance the speed of CPU. It is generally placed between Processor and Primary memory and acts as a buffer. It reduces the average access time to data from the main memory and is comparatively expensive.

Catch Memory Image Computer Organization Class 11 Notes

Control Unit

It controls the flow of data between input, process and output operations. It is responsible for coordination between the different units of a computer. Mostly all thin wires play the role of control unit.

Arithmetic Logic Unit (ALU)

Is responsible for actual processing of data. It retrieves the data from the storage unit and performs the arithmetic calculations and/or comparisons on them and the processed data is then sent back to the storage.

Output Devices

Devices used to display output like monitor or printer. Other forms of devices are not uncommon, for example speaker, plotter etc.

Block Diagram of Computer

Block Diagram of Computer Computer Organization Class 11 Notes

Computer Organization Class 11 Notes

Session 2: Components of Computer


It is the main circuit board where all hardware components like CPU, memory, hard drives, optical drives, network cards, video/audio expansion cards, various ports (such as USB, PS2), are mounted together to make a computer system function. It provides a connection to every component of the computer.

Input Devices

Input devices takes input from the user in the form of text, image, sound, video etc. a wide range of input devices have been devised for supporting varying types of input. Some of the input devices listed below:

Keyboard: this is a standard input device and takes data in the form of text/characters/numbers.

Mouse: it is a pointing input device used to point and select object.

Webcam: it is called as web camera and as it name suggest, takes data in the form of video/image.

Scanner: it generally stores data in the form of graphics. It actually converts and store any type  of hard copy like photograph, documents to soft copy as graphics.

Microphone : it is called as mic or mike and used for voice input/ audio input.

Output Devices

Devices that are used to give output in the form of visuals, text, audio, printout etc. different types of output devices are there to support various types of output. Some of the output devices are listed below:

Monitor/ VDU (Visual Display Unit): it is the standard output device and is similar to a television screen.

Speaker: it is an output device that gives output in the form of an audio/ voice.

Printer: It is also a standard input device which is used to take prints of any document, image, sheet etc.

Plotter: it is also a type of printer which is large in size and used to take prints of large maps, architectural designs.

Projector: it is an output device that gives an enlarged view of the output on a large screen. It is generally used for giving a view of output to a large audience.

CPU: it is Central Processing Unit which actually refers to Processor mounted in Motherboard. It is responsible for all kind of arithmetic and logical operations done for computer. CPU also ensures the coordination among all units of computer. Performance of any computer primarily depends on processor.
Processors can be classified on the basis of its speed and technology such as dual-core, cord-2-duo, quad-core, octa-core, PIV etc. Intel and AMD are two main manufactures of processor.
Speed of processors is usually measured in megahertz (MHz) – millions of instructions per second; and gigahertz (GHz) – billions of instructions per second, is indicative of its power.

Power Supply Unit

As it name implies, used to provide power supply to all different units of computer system. SMPS (Switch Mode Power Supply) is the device used as Power Supply unit. It converts high voltage AC to low voltage DC required by system.

Memory Unit

Random Access Memory (RAM): RAM is Primary memory which stores data temporarily. It is very important for well functioning of a computer system. Whenever we start computer system, operating system is loaded in the RAM. Any Application that we run, also first get loaded in the RAM. These days RAM of 8GB to 32 GB sizes are available for computer system. Programs get more space if More the RAM is, which leads to increased processing speed of the system.

Hard Disk (HDD): It is considered as secondary memory where all data and programs are permanently stored. C drive, D drive we see in computer, actually indicates a hard disk. Generally it is fixed inside CPU box but now a days external hard disks are also available with large sizes like 500GB, 1TB etc. when a program or data opens, it goes (occupy space) to RAM and return back (its address where it is saved) to hard disk, when closed. These days the capacity of a hard disk is expressed in terms of Gigabytes, Terabytes.

Pen drive/Flash drives: it is a small pen-like storage device of and can be accessed by directly inserting in the USB (Universal Serial Bus) Port. It is very popular these days because of its small size and easy accessibility.

Optical Storage devices: Compact disc (CD) and Digital Video Disc (DVD) are examples of optical storage devices. Capacity of a DVD is higher than that of a CD. Data in a Cd/DVD may be accessed by inserting the disc in a Disc Drive.

Units of Memory

Every bit of information in computer is stored in terms of Bits (Binary Digits) i.e. 0s and 1s.
1 nibble = 4 bits
1 byte = 8 bits
1024 bytes = 1 Kilobyte (KB)
1024 KB = 1 Megabyte (MB)
1024 MB = 1 Gigabyte (GB)
1024 GB = 1 Terabyte (TB)
1024 TB = 1 Petabyte (PB)
1024 PB= 1 Exabyte (EB)
1024 EB = 1 Zettabyte(ZB)
1024 ZB = 1 Yottabyte (YB)

Computer Organization Class 11 Notes

Session 3: Operating System

What is Operating System

  • The software that acts as an interface between user and computer hardware.
  • It is a System Software.
  • Every computer system must have at least one operating system installed.
  • Windows, Linux, Solaris, MAC OS, MS DOS are some of the examples of Operating System.
  • Gary Arlen Kildall is known as father of computer.
  • It helps in performing the core functionalities like accepting input from various input devices, directing the output to the display, managing the files and directories, communicating with hardware, and installing /uninstalling of peripheral devices.
Operating System Layer image Computer Organization Class 11 Notes
Operating System as an Interface

Functions of Operating System:

Functions of an Operating system can be broadly categorized as:

  • Communication Manager
  • Resource Management
  • Process Management
  • File Management
  • Memory Management
Operating System Functions Image IT 802 Class 11 Notes
Functions of Operating System

Communication Manager: Establishes communication between different peripheral devices like printer, mouse, keyboard, monitor etc. Operating System uses special programs called drivers to identify these devices and their properties, to interact with them.

Resource Management: Here resource management refers to managing allocation and priority of different resources such as memory, CPU time, files, Input/output devices etc., to the various processes to get an optimum performance from the system. All these are discussed below:

Process Management: it refers to managing, controlling and scheduling different operations being executed in the CPU. It decides which process gets the processor and for how long.

Memory Management: it refers to dynamically allocating memory to the process to be executed and release when not needed.

File Management: It refers to managing all the files and folders in secondary memory. Creating, deleting, moving, copying or renaming are some common task performed on files.

Types of Operating system

Operating systems can be classified in different ways as given below:

Single Tasking and Multi-tasking

Single Task Operating System: such operating systems allow execution of only a single program at any given point of time.
Multi-Tasking operating system: can execute more than one program simultaneously. The processor time, in this case, is divided amongst various processes.

Single User and Multi-user

Single-user operating systems allow only one user to use the system. The desktop systems can be classified as typical single user systems.
Multi-user operating systems allow many users to access the system by maintaining an account of all the registered users.

Real-Time Operating System

It is designed for computer applications or software that requires a response within a specified time frame in order to function properly. For example, an anti-aircraft missile system must fire as soon as it receives a signal from the enemy aircraft, before it leaves the bomb and flies away.

Batch Processing Systems

Batch processing system means to take all types of programs and data in batch form and then proceed to process. The main purpose of using a batch processing system is to reduce the set up time while submitting similar tasks to the CPU.

Computer Organization Class 11 Notes

Session 4: Troubleshooting and utilities

Common Troubleshooting Steps

When system boots and all peripheral devices have been successfully detected, most systems will produce a beep. If any connected device (such as monitor, keyboard, mouse, and printer) does not switch on, than try the following:

  • Close running programs that are not being currently used
  • Check the cable of the specific computer hardware which is not working. Ensure that all connections are tightly and correctly plugged in, and the Power button of these devices is ON. For wireless devices, make sure it is turned on and the batteries are charged.
  • Repeat the sequence of steps that you performed before the problem occurred. Observe if it causes the same response from your computer.
  • Access the Help window by pressing the F1 key. This window helps to find a solution to the problem.
  • Record the full error message for future reference.
  • Restart the peripheral device. If the device still does not switch on, shut down the computer and start it again.

Troubleshooting Hardware Problem

Monitor is not Showing any Display/ The Screen is Blank

  • The computer may be in Sleep mode. Click the mouse or press any key on the keyboard to wake it up.
  • For a desktop, ensure a proper connection of a cable connecting the monitor and a computer cabinet. Check that the power cables of the monitor and cabinet are plugged into the electric socket and the power is turned on.
  • The laptop’s battery could be very low, causing the laptop to switch of f. Connect the charging cable to the laptop and plug it into the electric socket. The laptop will start charging, and in a few minutes, the laptop can be switched on.

Keyboard Troubleshooting
If  the keyboard is not responding, try the following:

  • Check Connections: Check the connection of the keyboard to the computer. If it is not connected, or the connection is loose, connect it properly to the computer.
  • Check for any Damage: Inspect the keyboard cord for any damage. If any damage is found, the keyboard may need to be repaired or replaced.
  • Change Batteries: For a wireless keyboard, the batteries may have discharged. You may need to change the batteries.
  • Keys are stuck: If one of the keys on your keyboard is stuck, you need to clean the keyboard.

Mouse Troubleshooting
In case the mouse is not working, try the following troubleshooting options:

  • Check Connections: Make sure that the mouse is securely plugged into the computer.
  • Check for any Damage: Inspect the mouse cord for any damage. If the damage is noticed, the mouse may need to be replaced.
  • Check the Cordless Mouse: For a cordless mouse which is not working, switch off, and then switch on the cordless mouse. This should re-establish a connection with the system.
  • Clean the Mouse: Try cleaning the mouse with a damp cloth. Clean the area around the button located on the underside of the mouse.

Troubleshooting Printer Problems

Printer is Not Responding (Not Printing)
The printer could not be responding due to a number of reasons. Check for each of the following causes, taking necessary action as required:

  • The Printer is Not Connected Properly or Not Switched On: Ensure that the printer cables are connected properly. If the printer is not switched on, switch it on.
  • The Printer is Out Of Paper: If the printer does not have paper, put paper in the paper tray and try printing again.
  • The Printer Paper Jam (Paper is caught in the Printer): Open the printer and remove the paper caught in the printer. Close the printer and try printing again.
  • The Ink Cartridge of Printer is Empty: Most printers give a warning message when the ink levels are low (insufficient for printing). Change the ink cartridge and try again.
  • Incorrect Printer Driver: The printer driver may be incorrect. You would need to install a new printer driver. The latest driver can be downloaded from the manufacturer’s website.
  • The Printer and Computer are not Communicating Properly: This problem is more common when a wireless connection is being used to connect a PC/ laptop to a printer. Check that the IP address configured on your computer matches the Dynamic IP address allocated to the printer.

Print Jobs are Being Sent to the Wrong Printer

When there are multiple printers on a network, a possible problem could be that a print job is being sent to a wrong printer. This is because your system has set the default printer as Printer A, but you had actually wanted the print job to go to Printer B. You could either change the default printer to Printer B or choose Printer B for the current job.

Hot to change the Default Printer

  • To change the Default Printer, open the devices and printer dialog box. Click Start button> Control Panel > Hardware and Sound > Devices and Printers. Alternatively, click Start button > Control Panel > All Control Panel Items > Devices and Printers > A dialog box opens.
  • There is a tick inside a small green circle next to its icon (this signifies that Printer has been set as the default printer).
  • Right click on the icon for the printer you want to set as default, a pop-up menu is displayed. Select, Set as default printer from this pop-up menu. The tick next to the printer you selected shows that it is now the default printer.

Printer is Slow

The printing speed can be improved by reducing the printing quality and using Fast Draft/ Fast Printing. This works well for everyday printing. Change the default printer quality setting from Normal to Fast Draft.

Sound Troubleshooting

When you are not getting sound from the speakers, troubleshoot using the suggestions given below:

  • Check Speaker Volume: Check the volume level of the speakers. Click the Audio button in Task Bar to make sure the sound is turned on and that the volume is up.
  • Check Audio Player Controls: Many audios and video players have their own separate audio controls. Ensure that the sound is turned on and that the volume is set large enough to be heard.
  • Check the Cables: In case external speakers are used, ensure that the speakers are plugged into the electric socket, turned on, and connected to the correct audio port or a USB port on your system. If your computer has color-coded ports, the audio output port will usually be green.
  • Check the Sound Using Headphone: Connect headphones to the audio output port of your computer, and check whether you can hear sound from the headphones. If you can, that means there is something wrong with your speakers. Contact a Service Engineer.

Troubleshooting Software Problems

An Application is Running Slow

Check for Available Updates: Sometimes applications run slow due to asking for updates. So to check for updates, Click the Help menu and look for an option to check for Updates. In case this option is unavailable, you can search online for application updates.
An Application is Frozen: Sometimes an application may freeze. When this happens, you will not be able to close the window or click any button within the application. Than you can try following troubleshooting options:

  • Forcefully End the Application by opening task manager by pressing Ctrl+Alt+Delete and select the application not responding and click on ‘End Task’. Now restart application.
  • Restart the Computer: If you are unable to forcefully end an application, close all running programs and restart the computer.
  • If you are unable to shutdown/ restart your system, perform a hard reboot by pressing the Power button, i.e. manually turn off the computer. Remember that hard reboot may cause data loss.

Once the system is responding, run the virus check to scan the system for viruses.

Utilities Applications

Utilities are the special programs that help computer systems to work more smoothly, efficiently and effectively. Utility software programs help in :

  • improving the performance of computer
  • provide security from virus,
  • manage disk space
  • free disk space on hard Disk – provide backup etc.

Disk Cleanup Utility

We can use Disk Cleanup utility to get some more space for smooth functioning of computer as sometimes due to non-availability of free space slows the functioning of the computer. There should be at least 200-500MB of free hard drive space on your system.

To run the Disk Cleanup Application follow given steps:

  • Open ‘This PC’ or ‘My Computer’ window and highlight the C drive.
  • Right click on C drive and select the Properties option from pop-up menu appeared. A dialog box opens as given below.
  • Now from ‘General’ Tab of this box Select ‘Disk Cleanup’ to start application.
  • From Disk Cleanup box as given below click on Clean up system files button. This will delete any unnecessary system-related files from the local disk.

Empty Your Recycle Bin

This can be done by right-clicking on the Recycle Bin icon (usually on the desktop), and then selecting Empty Recycle Bin.

Remove Temporary files

It is important to periodically remove the temporary files and the Internet browsing history. This too will increase the free space on your disk.
To do this open Disk Cleanup application as mentioned before and select ‘temporary Internet Files’ from the dialog box given below and than select OK.

Disk Defragmentation

The information in our files changes frequently. This results in gaps or spaces in the file stored in the memory (hard disk). The file thus takes more space on the computer, and may cause the computer to slow down. You need to run a Disk Defragmentation program to reclaim these gaps in space. This can be achieved as follows.

  • Open ‘This PC’ or ‘My Computer’ window and highlight the C drive.
  • Right click on C drive and select the Properties option from pop-up menu appeared. A dialog box opens as given below.
  • Select ‘Optimized’ option from Tool Tab  of the dialog box as given below.
  • Now disk defragmentation dialog box opens as given below.
  • From here select the drive you want to optimize and click on ‘optimize’.
  • After sometime defragmentation will be done.

Troubleshooting Networking Problems

Unable to Connect to the Network

Checking for Network Connectivity: To check the internet connection, view the Network icon (triangular in shape) on the Task Bar (bottom right of the screen) as given below. This figure shows that there is no network connection (an orange star on the network icon).

An alternate method to check for network connectivity is to click Start button > Control Panel > Network and Sharing Centre as you can see in picture given below. The Red Cross between the USER-PC and Internet shows that the computer is not connected to the Internet.

Now to find the cause of the Network Connectivity problem Select ‘Troubleshoot Problem’. The troubleshooting application will display a few screens while the system attempts to diagnose the issue: Windows Network Diagnostics: Investigate router or access point issues, Detecting problems, Resolving the problems, Detecting additional problems, etc. These screens will guide you in establishing a connection.

If you are still unable to connect to the internet, the troubleshooting application would report the Problem in network connectivity.

Check for the Validity of IP Address

If the above steps do not help in establishing a network connection, you would have to check a few more system settings.

First check the validity of the IP address of your system. In the bottom left corner of your Windows screen click Start. In the Search box type CMD and press Enter.

The COMMAND PROMPT (an MS-DOS window) will open. Type IPCONFIG and press Enter. The results should show the Connection-specific DNS Suffix, IP Address, etc., as seen in image given below. This information will only show if your system is connected to the internet, else, it will show Media State: Media disconnected.

The Network Fly lead is Not Working Properly

The fly lead is the cable that connects the network card in your computer to a network point (usually on the wall). A non-operational network fly lead could also cause failure in the internet connection. The network fly lead is seated in the network slot on your computer. In this situation Seek assistance from a network administrator.

The Network Card is Not Working Properly

A working network card is essential to connect to the Internet. The network card lights must be flashing or lit up. If there are no lights, either the network card is broken, or there is no network to connect to. A broken network card needs repair or replacement. Contact a Service Engineer.

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