Comprehensive Computer System Class 11 Notes Chapter 1

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Computer System Class 11 Notes Computer Science Chapter 1

Chapter 1 : Computer System

Introduction to Computer System

A computer is an electronic device that can be programmed to accept data (input), process it and generate result (output). It consists of hardware and software that work together to perform tasks. Following figure shows the block diagram of a computer system.

Computer System Class 11 Notes

Components of Computer System

1. Central Processing Unit (CPU) :

It is the component of a computer that carries out the actual processing and usually referred as the brain of the computer. CPU has two main components — Arithmetic Logic Unit (ALU) and Control Unit (CU). ALU performs all the arithmetic and logical operations while CU controls sequential instruction execution. CPU is also popularly known as microprocessor.

During processing, the CPU stores the data as well as instructions in its local memory called registers. Registers are part of the CPU chip and they are limited in size and number.

2. Input Devices :

The devices through which signals are sent to a computer are termed as input devices. for example Keyboard, Mouse, Scanner etc. Braille keyboards are used to help the visually impaired for entering data into a computer.

Data entered through input device is temporarily stored in the main memory (also called RAM) of the computer system. For permanent storage and future use, the data as well as instructions are stored permanently in additional storage locations called secondary memory.

3. Output Devices :

The devices that receives data from a computer system for display, physical production, etc. are called output device. for example Monitor, Printer, Speaker etc.

A printer is the most commonly used device to get output in physical (hardcopy) form. There are three types of commonly used printers which are inkjet, laserjet and dot matrix. Now-a-days, there is a new type of printer called 3D-printer, which is used to build physical replica of a digital 3D design.

NOTE: A braille display monitor is useful for a visually challenged person to understand the textual output generated by computers.

Computer System Class 11 Notes

Computer Memory

A computer system needs memory to store the data and instructions for processing. There are two types of memory

1. Primary Memory :

It is also called main memory. Program and data are loaded into the primary memory before processing. It is of two types viz. (i) Random Access Memory (RAM) and (ii) Read Only Memory (ROM).

RAM	ROM
It stands for Random Access Memory	It stands for Read Only Memory
It is temporary memory.	It is permanent memory.
Data will be wiped out as the power supply is turned off.	Its contents are not lost even when the power is turned off.

Computer System Class 11 Notes

Cache Memory

Cache memory is a small and very fast memory located between the CPU and RAM. It store copies of data that the CPU uses very frequently.

When the CPU needs some data:

It first checks the cache memory.
If the data is found there, it uses immediately and saves time
If the data is not in the cache the CPU gets it from the main memory which is slower(taking more time)

2. Secondary Memory :

This memory is used to store the data or instructions for future use. The secondary memory is non-volatile and has larger storage capacity than primary memory. It is slower and cheaper than the main memory. Examples of secondary memory devices include Hard Disk Drive (HDD), CD/DVD, Memory Card, etc.

Computer System Class 11 Notes

Units of Memory

A computer system uses binary numbers to store and process data. The binary digits 0 and 1, which are the basic units of memory, are called bits. A 4-bit word is called a Nibble. Examples of nibble are 1001, 1010. A two nibble word, i.e., 8-bit word is called a byte, for example, 01000110, 01111100, 10000001, etc.

Computer System Class 11 Notes

What is Software :

The software comprises a set of instructions which on execution deliver the desired outcome. It is that component of a computer system, which we cannot touch or view physically.

Some examples of software include operating systems like Ubuntu or Windows 7/10, word processing tool like LibreOffice or Microsoft Word, video player like VLC Player, photo editors like GIMP and LibreOffice draw.

A document or image stored on the hard disk or pen drive is referred to as a soft-copy. Once printed, the document or an image is called a hard-copy.

What is the need of Software

The main role of a software is to make the computer hardware useful and operational. We cannot instruct the hardware of a computer directly. Software acts as an interface between human users and the hardware.

The software can be broadly classified into three categories viz. (i) System software, (ii) Programming tools and (iii) Application software.

(i) System Software :

The software that provides the basic functionality to operate a computer by interacting directly with its constituent hardware is termed as system software. Examples of system software are operating systems, system utilities, device drivers, etc.

(A) Operating System : As the name implies, the operating system is a system software that operates the computer. An operating system is the most basic system software. It is an interface between the user and hardware. Some of the popular operating systems are Windows, Linux, Macintosh, Ubuntu etc.

Functions of Operating System :

It manages all the resources of a computer, i.e., its hardware including CPU, RAM, Disk, Network.
It act as an interface between user and computer.
It provide services for applications software.

Computer System Class 11 Notes

(B) System Utilities : Software used for maintenance and configuration of the computer system is called system utility. Some system utilities are shipped with the operating system for example disk defragmentation tool, formatting utility, system restore utility.

There are other set of utilities which are not shipped with the operating system but are required to improve the performance of the system, for example, anti-virus software, disk cleaner tool, disk compression software, etc.

(C) Device Drivers : As the name signifies, the purpose of a device driver is to ensure proper functioning of a particular device. The device driver acts as an interface between the device and the operating system. Just
like a language translator, a device driver acts as a mediator between the operating system and the attached device.

(ii) Programming Tools : In order to get some work done by the computer, we need to give instructions. Computer languages are developed for writing these instructions. Humans are able to write programs in high-level language while computers understand machine language. There is a continuous need for conversion from high level to machine level language, for which translators are needed.

(A) Classification of Programming Languages : It is very difficult for a human being to write instructions in the form of 1s and 0s. So different types of computer programming languages are developed to simplify the coding. Two major categories of computer programming languages are low-level languages and high-level languages.

Low Level Language	High Level Language
machine dependent languages	machine independent
Execution is faster	Execution is slower
Do not need language translator	Needs Language translator
Low-level languages include Machine Language and Assembly Language	high level language include C++, Java, Python, etc.

Computer System Class 11 Notes

Computer System Class 11 Notes

(B) Language Translators : As the computer can understand only machine language, a translator is needed to convert program written in assembly or high level language to machine language. The program code written in assembly or high-level language is called source code. The source code is converted by a translator into the machine understandable form called object (machine) code.

The three types of translators used in computing systems are assembler, compiler and interpreter.

Assembler : The translator used to convert the code written in assembly language to machine language is called assembler.

Compiler : It converts the high level language to low level language (machine language) in one go.

Interpreter : It converts the high level language to low level language (machine language) line by line

Interpreter	Compiler
It converts the high level language to low level language (machine language) line by line.	It converts the high level language to low level language (machine language) in one go.
It is slower	It is faster
It stops at first error, shows errors one by one	It shows all errors together at the end

(C) Program Development Tools : Whenever we decide to write a program, we need a text editor where we type instructions and store the file as the source code. Then an appropriate translator is used to get the object code for execution.

In order to simplify the program development, there are software called Integrated Development Environment (IDE) consisting of text editor, building tools and debugger. Python IDLE, NetBeans, Eclipse, Atom, Lazarus are few examples of IDEs.

NOTE: Debugger, as the name implies, is the software to detect and correct errors in the source code.

Computer System Class 11 Notes

Application Software :

Those software which are designed to perform specific task for the end users are called application software like Microsoft word, Microsoft excel etc. There are again two broad categories of application software—
general purpose and customized application software.

(A) General Purpose Software : The application software developed for generic applications, to cater to a bigger audience in general are called general purpose software. Adobe Photoshop, GIMP, Mozilla web browser, iTunes, etc.

(B) Customized Software : These are custom or tailor-made application software, that are developed to meet the requirements of a specific organization or an individual. They are designed as per user requirements. for example school management software, accounting software etc.

Proprietary or Free and Open Source Software :

Those software whose source code is available with an aim to develop and improve further with each other’s help. Such software is known as Free and Open Source Software (FOSS). examples of FOSS include Python, LibreOffice, Open office, Mozilla Firefox.

Sometimes, software are freely available for use but source code may not be available. Such software are called freeware. Examples of freeware are Skype, Adobe Reader.

When the software to be used has to be purchased from the vendor who has the copyright of the software, then it is called proprietary software. Examples of proprietary software include Microsoft Windows, Tally, Quick heal, etc

Operating System :

An operating system (OS) can be considered to be a resource manager which manages all the resources of a computer, i.e., its hardware including CPU, RAM, Disk, Network.

OS User Interface :

There are different types of user interfaces each of which provides a different functionality. Some commonly used interfaces are :

(A) Command-based Interface : Command-based interface requires a user to enter the commands to perform different tasks like creating, opening, editing or deleting a file, etc Examples of operating systems with command-based interface are MS-DOS and Unix.

(B) Graphical User Interface : Graphical User Interface (GUI) lets users run programs or give instructions to the computer in the form of icons, menus and other visual options. GUI interfaces include Microsoft Windows, Ubuntu, Fedora and Macintosh etc.

(C) Touch-based Interface : Using the touchscreen, a user provides inputs to the operating system, which are interpreted by the OS as commands like opening an app, closing an app, dialling a number, scrolling across apps, etc. Examples of popular operating systems with touch based interfaces are Android and iOS.

(D) Voice-based Interface : Now a days user can use voice-based commands to make a computer work in the desired way. Some operating systems which provide voice-based control to users include iOS (Siri), Android (Google Now or “OK Google”), Microsoft Windows 10 (Cortana).

(E) Gesture-based Interface : Some smartphones based on Android and iOS as well as laptops let users interact with the devices using gestures like waving, tilting, eye motion and shaking.

Computer System Class 11 Notes

Disclaimer : I tried to give you the appropriate and to the point handouts of ” Computer System Class 11 Notes ” , but if you feel that there is/are mistakes in the handouts of “Computer System Class 11 Notes “ given above, you can directly contact me at csiplearninghub@gmail.com. Above article on “Computer System Class 11 Notes” are taken from NCERT Computer Science Book