CBSE Computer Science (083) Class XI Chapter 1

1. Computer System Overview
Made By: Tarun Baria, PGT CS,
JNV Leh

2. What is Computer?
A computer is a programmable electronic device that accepts raw data as
input and processes it with a set of instructions (a program) to produce the
result as output.

3. Two Components of Computer:
● Hardware
○ The physical electronic components of a Computer
● Software
○ Recorded instructions and programs to govern the working of the Computer

4. Basic Computer
Organization

5. Basic Computer Organization

6. Input Unit

7. What is Input Unit?
● Formed by Input Devices attached to the Computer
● Takes Input and converts it into computer understandable form (In binary
form)
● Computer Input also consist of Data and Instruction

9. Output Unit

10. What is Output Unit?
● Formed by Output Devices attached to the Computer
● The output that computer generates is in Machine Language (e.g. Binary
Language)
● The Output Devices converts the output data into Human Understandable
form and presents it to the User

12. CPU (Central Processing Unit)

13. What is CPU?
● It is the Main Control and Processing Unit of the Computer
● Brain of the Computer
● Components of the CPU:
○ ALU (Arithmetic and Logical Unit)
○ Control Unit
○ Registers

14. ALU
● Performs four arithmetic
operations (+, -, x, /)
● Performs some logical
operations (<, >, <=, >=, !=)
● Decision making takes place
in ALU of the CPU
Arithmetic and Logical Unit

15. CU
Control Unit
● Controls and Guides the
interpretation, flow and
manipulation

16. Registers
● Small Units of Data Holding
places located near the
Processor
● Used to store some
important instructions and
important data when CPU is
running some Program
● Frequently Used
instruction/Memory is stored
in Registers and rest of the
instruction/data is stored in
Cache,RAM, etc…

17. Memory (Main Memory/Primary Memory)

18. What is Primary Memory?
● A predefined working place where it temporarily stores data/programs
which are running at the time.
● The memory is cleared once the program is done executing
● The memory is addressed till every last bit. Data is stored in the memory
in binary language

19. Units of Computer Memory
Size Unit Name
1 Bit 1 Bit Bit
4 Bits 1 Nibble Nibble
8 Bits 8 Bits Byte
210 (1024) Byte 1KB Kilo Byte
210 (1024) KB 1MB Mega Byte
210 (1024) MB 1GB Giga Byte
210 (1024) GB 1TB Terra Byte
210 (1024) TB 1PB Peta Byte
210 (1024) PB 1EB Exa Byte
210 (1024) EB 1ZB Zeta Byte

20. Parts of Primary
Memory ● Random Access Memory
(RAM)
● Read Only Memory (ROM)

21. Random Access Memory (RAM)
● In RAM, memory cells can be accessed for information transfer from any
desired random location. Hence the name, Random Access.
● It is volatile memory (Meaning it gets erased as soon as the power goes
off)
● There are two basic types of RAM:
○ Dynamic RAM
○ Static RAM

22. DRAM
● Made of Transistors and Capacitors
● Memory Access Time is 20 to 70
nanoseconds
● Used widely in most computers
● Made of flip-flops
● Memory Access Time is about 10
nanoseconds
● Used in specialised applications
SRAM

23. Read Only Memory (ROM)
● We cannot perform write function on ROM
● In ROM, the data is permanently written during the time of production. It
cannot be erased or altered, can only be Read.
● It is non-volatile in Nature
● Slower than RAM

24. Types of ROM
● PROM (Programmable ROM)
○ Also called OTP (One TIme Programmable)
○ Information can only be burned in PROM for single time using ROM burner
● EPROM (Erasable Programmable ROM)
○ Can be erased for many times. But Data can only be erased fully.
○ UV - EPROM takes upto 20 minutes to erase the EPROM
● EEPROM (Electrically Erasable Programmable ROM)
○ Data is erased electrically, which is faster
○ Partial data can be erased
● Flash EEPROM
○ Like EEPROM, but faster (takes less than second to erase)
○ Does not erase partially, erases fully
● Mask ROM
○ The contents of the Mask ROM are programmed by IC Manufactured itself and cannot be
altered by a programmers

25. Storage Unit

26. Why do we need Storage Unit?
● Primary Memory has limited storage
capacity
● Primary Memory cannot store data
permanently
● Hard Disks
● Compact Disks
● DVDs
● Flash Memory
● Blue Ray Disc
Different types of Storage

27. Hard Disc Drive (HDD)
● Circular Platters situated in the
disc spin continually and store
data in magnetic form.
● It can have storage capacity
varying from several GBs to TBs

28. Compact Disks (CDs)
● It is optical media
● Relatively Cheap and offers storage upto
700 Mb
Types
● CD - ROM (Read Only Memory)
○ Data is stored at production time and
cannot be erased or reused
○ Used for distribution (eg. softwares,
games, e-books etc)
● CD - R (Recordable)
○ Can be written on only once.
● CD - RW (Re-Writable)
○ Erasable disc, can be erased and written
on multiple times

29. Digital Versatile Disks (DVDs)
● It is optical media
● Can hold upto 15 times more storage
than CD (15 times more)
● 20 times faster than CD
● Also called Super Density Disk
Types
● DVD - ROM (Read Only Memory)
○ Data is stored at production time and
cannot be erased or reused
○ Used for distribution (eg. softwares,
games, e-books, movies etc)
● CD - R (Recordable)
○ Can be written on only once.
● CD - RW (Re-Writable)
○ Erasable disc, can be erased and written
on multiple times

30. Blue Ray Disc (BD)
● Optical Media Storage Drive
● Same Dimensions as CD or DVD
● CD and DVD works on Red Lasers which
have bigger wavelength
● Blue Ray works on Blue to Violet
wavelengths which has smaller
wavelengths hence more data can be
stored in same space
● Can store upto 128 GB of data

31. Flash Memory
● Small, Ultra Portable Storage Device
● Storage is done in ‘solid state’, i.e. it
does not use magnetism nor it uses
optics (lasers)
● Works similarly as RAM, but it can retain
data even when power is switched off
● Inexpensive and more durable
compared to HDDs
● Can store data in volume of few GBs to
TBs
HDD
SSD

32. The System Bus

33. The System Bus
An electronic pathway composed of
connecting cables and that connects the
major components of a computer
Data and Instruction are passed among the
computer system components through
system bus
Different System Buses:
● Data Bus: Carries Data
● Control Bus: Carries control
instructions
● Address Bus: Carries addresses
● I/O Bus: Connects input, output and
other external devices to the system

34. Types of Software

35. Hardware vs. Software
● Hardware represents physical and tangible components of the computer.
I.e. those which can be touched
● Software represent the set of programs that govern the operation of a
computer system and make the hardware run
○ Softwares can be broadly classified into two types:
■ System Software
■ Application Software

36. System Software
● Computer is nothing but a
machine that does not know
anything by itself. It requires
directions/Instructions in
order to perform the
operations.
● The software which control
the internal computer
operations is known as
System Software
Two Types:
A. Operating System
B. Language Processor

37. A. Operating System
● The goal of the OS is to -
○ Make Computer System convenient to use
○ Use computer hardware in efficient manner
● OS is the most important component of the computer which controls all
the components of the computer system
● Major components of computer system are:
○ Hardware
○ OS
○ Application Program
○ Users

38. How Computer Actually Works
● The hardware provides basic computing resources
● The application software provides the ways to solve the computing/other
problems of the user
● Operating System controls and coordinates the use of hardware among
the various application programs for the various users
● …Learn by yourself!!!
● More in Chapter 4!

39. Types of OS
● Single User OS
● Multiuser OS
● Time Sharing OS
● Real Time OS
● Multiprocessing OS
● Distributed OS

40. B. Language Processors
● Language Processor is a special type of Computer Software that can
translate the source code into an object code
○ What is Source Code?
■ It refers to a program/code written by a programmer in high level language eg.
Python or JAVA or C++ (which is understandable by human/programmer)
○ What is object Code?
■ A code written in machine language or binary code which a machine (computer) can
understand
● More in chapter 4!

41. Types of Language Processors
1. Assembler:
Language Processor that converts assembly language code into machine
language code
1. Interpreter:
A type of system software that translates and executes instructions written in
computer program` line by line/unit by unit
1. Compiler:
A system software that translates and executes instructions written in a
computer program in a one go
● More in Chapter 4!

42. Application
Softwares
● This type of Software pertains
to one specific application
● These programs are written
by programmers to perform
a specific type of task, eg -
○ Word Processing
○ Photo/VIdeo Editing
○ Tickets Booking
○ Financing
○ Any other application that you
can think of
● Application softwares are
written to make computers
useful for users
Can be divided into 4 Categories:
1. Packages
2. Utilities
3. Customised Software
4. Developer Tools

43. 1. Packages
● Some general softwares are designed that may be used by individual
users in a manner that it suits their requirements. Such general
application softwares are called packages
● eg
○ Word Processing Software
○ Spreadsheets
○ DBMS
○ Graphics Designing Software

44. 2. Utilities
● Those helpful programs that ensure the smooth functioning of the
Computer
● Utility Programs are meant to assist your computer
○ Text Editor
○ Backup Utility
○ Compression Utility
○ Disk Defragmenter
○ Anti Virus

45. 3. Customized Software
● These softwares are specially created to fulfill the business requirement
● eg.
○ Hotel Management and Reservation
○ Finance/Accounting
○ Inventory Management
○ tailor - made softwares

46. 4. Developer Tools
● These softwares help programmers when they are writing programs or
developing softwares
● Developer tools are set of codes/functions/scripts/classes etc…

47. Quiz Winners
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48. Thank You!