Computer Science

Computer Science is a scoring topic in SSC CGL, contributing 2 to 4 questions every year primarily in Tier-I and Tier-II. Questions are direct and factual - covering CPU, memory, operating systems, programming languages, networking, internet, and abbreviations. Students who memorize the key facts and full forms in this chapter will find these questions very easy to answer correctly.

1. Computer - An Introduction

1.1 What is a Computer?

• A computer is an electronic device that processes data according to a set of instructions
• It receives input, processes it, stores it, and produces output
• CPU (Central Processing Unit) is also known as the Brain of the Computer
• CPU is the part where the main work of computation happens
• It functions like a central data analyzer unit
• It is the part where the computer receives data and analyzes instructions

1.2 Components of CPU

The three main components of CPU are:

1. ALU (Arithmetic Logic Unit) - performs arithmetic (addition, subtraction, etc.) and logical operations (AND, OR, NOT)
2. Control Unit - controls all other parts; manages the flow of data
3. Memory Unit (Registers) - holds data temporarily during processing

1.3 Wetware

• In the context of computers, Wetware is called the human brain
• It is a biological computer made with the help of living neurons
• Also known as Artificial Carbon Brain or Neurocomputer

1.4 Emulator vs Simulator

• Emulator: A program made to copy the function of one system on another system
• Simulator: A program that runs computer games
• Evaluator: Used to measure the capability performance of a computer
• PCB (Printed Circuit Board): Creates pathways (Pathway) in computers

1.5 CPU Scheduler

• CPU Scheduler is also known as Short-Term Scheduler
• It performs all types of data processing
• It stores intermediate results and instructions
• It controls the operation of all parts of the computer

1.6 Data Hazard in Computer Science

• In computer science, Data Hazard is the situation when a pipeline changes the order of read/write access for operations

2. Development of Computer

2.1 Generations of Computers

• Third Generation (1965-1975): IC (Integrated Circuit) started being used
• IC (Integrated Circuit) was invented by Jack Kilby of Texas Instruments
• Third generation computers were lighter in size and weight and more reliable than first and second generation

3. Memory

3.1 Types of Memory

3.2 Cache Memory

• Cache Memory is a high-speed semiconductor memory that can increase the speed of the CPU
• It works as a buffer between CPU and Main Memory (RAM)
• It is used to store input given by the user
• It is the fastest memory that provides high-speed data access to the computer microprocessor
• Cache Memory works on the principle of Reference

3.3 Cache Memory - Between Which Components?

• Cache Memory works between CPU and RAM

3.4 Write-Back Method

• When a word is removed from cache, the method of updating main memory is called Write-Back

3.5 RAM (Random Access Memory)

• RAM (Random Access Memory) is a type of computer data storage that stores program instructions frequently used to increase the system's normal speed
• It is temporary/volatile memory - data is lost when power is off

3.6 Micro-Operation

• Operations performed on data stored in registers are called Micro-Operations
• In Micro-Operation, the CPU instructs the central processing unit micro-operation complex machine to apply the instructions in detail

3.7 Associative Memory

• In information technology, Associative Memory is called Content Addressable Memory
• When information is saved in a definite place or received from a definite place, the place where it is stored is called Associative Memory

3.8 Garbage Collection

• The process of going through the entire file system, marking any file/folder that can be accessed, is called Garbage Collection
• It is a self-memory management technique that stores unnecessary data that will not be used in future as a pool or heap

3.9 Flip-Flop

• For storage of one bit data, Flip-Flop circuit is used
• In electronics, Flip-Flop is a digital circuit whose output stays in one of two stable states

3.10 Page Fault

• Page Fault occurs when a program reaches a page that is not in main memory at that time

4. Design Tools and Programming Languages

4.1 C Language and Unix

• 'C' is a commonly used computer programming language
• Developed by Dennis Ritchie at Bell Telephone Laboratory in 1972
• Purpose: To create the UNIX operating system
• UNIX is the first operating system written in high-level language (C Language)
• Its use is mainly for web servers

4.2 Types of Operating Systems

• Linux is an Open Source Operating System
• Windows Operating System belongs to Microsoft Company
• Current latest: Windows 11 (at time of writing)
• C++ is a type of computer language also called Programming Language
• Other computer languages: A+, A++, COBOL, BASIC, etc.

4.3 Query Language

• Query Language provides the computing facility to search and retrieve information
• It is a database programming language

5. Data Representation and Number System

5.1 Keys in Database

There are primarily 4 types of Keys:

• Primary Key - to preserve records; it is also a Candidate Key
• Foreign Key - every relation has at least one Foreign Key
• Candidate Key - one that can fulfill all needs
• Alternate Key
• A Primary Key is also a Candidate Key

6. Software

6.1 Computer Virus

• A Computer Virus is a program that can make copies using its own location, and can infect a computer without the user's permission
• For self-replication of computer virus, the technique of Spawn is used
• A virus can spread from one computer to another only when its host is brought from an uninfected computer

6.2 Daemon

• A Daemon is a continuously active system program of a system
• It is an operating system or computer program of a multi-purpose computer that runs as a background process (background process) rather than being under direct control of a user
• Daemon helps to establish coordination with other computers on a network while also responding to e-ware activity

6.3 Operating System vs Web Browser

• Android, Vista, iOS are Operating Systems
• Opera is a Web Browser (NOT an operating system)
• Other Web Browsers: Google Chrome, Mozilla Firefox, etc.

7. Data Communication

7.1 Protocol

• Protocol determines the way of communication
• Protocol is a set of rules that helps two devices to successfully connect and transmit data
• Using Protocol, data is exchanged in a computer network
• Each protocol has a different way

7.2 Important Protocols

• HTTP was invented by Ted Nelson in 1965
• UDP (User Datagram Protocol) is a Connectionless Protocol
• UDP is designed by David P. Reed
• It uses a connectionless transmission model of minimum protocol mechanism
• UDP is often sent as CL-mode communication

7.3 Optical Fiber

• In Optical Fiber, signals are transmitted by Total Internal Reflection
• Optical Fiber was proposed in England's ASTC Laboratories by Charles Kao and George Hockham in 1966
• Successfully developed by Corning Glass Works in 1970
• Information is sent as light points through total internal reflection

7.4 Network Congestion

• When the network cannot deliver data due to excessive data being sent by many computers inside a network, it is called Network Congestion
• To stop Network Congestion, the process of Congestive Collapse is adopted

7.5 Network Devices and Layers

• Repeater: An electronic machine that receives signals and transmits them forward
• Router: Used to connect many networks; also used to find various routes

7.6 Routing Algorithm

• The algorithm used to decide the path of transferring packets from source to destination is called Routing Algorithm (Path Direction/Marg Nirdesh)

7.7 Token

• Brief message in a network going from one station to another station is called Token
• Token is a chain of bits that flows in a network ring
• If a network system has a token, it can send information to another computer
• Since a network chain has only one token, only one computer can send information at a time

7.8 Multicast

• Sending a frame to a group of stations is called Multicast
• Multicast is communication between one sender and multiple receivers on a network
• Wireless cellular digital packet data technology is supported through Multicast

7.9 Cloud Computing

• Cloud Computing performs computation, storage, and even application as a service across the entire network
• Cloud Computing is a part of computing

8. Internet

8.1 Internet Users

• Country with maximum internet users: China (about 52.3% of population)
• After China, India has about 36% of population as internet users
• United Kingdom has the highest percentage (93.5%) but much smaller population

8.2 IMPS

• Transfer of money through mobile is called IMPS (Immediate Payment Service)
• Started: 22 November 2010
• Operated by: NPCI (National Payments Corporation of India)

9. Abbreviations

• IC in Electronics = Integrated Circuit (also known as Microchip)
• It is an electronic circuit built inside a semiconductor material
• Contains resistors, capacitors, diodes, transistors and other semiconductor components

9.1 WIMAX

• Full form of WIMAX: Worldwide Interoperability for Microwave Access
• WIMAX is a telecommunications technology
• Through this technology, one computer can establish contact with another computer without the help of wires
• It works on both Internet and Cellular networks
• This service was first started in Jaipur in India

10. Miscellaneous

10.1 Data Integrity

• In IT, Data Integrity means that data available in the database is correct and consistently complete
• In a database management system, data should not be duplicated and data should be consistent
• So that data is not lost and data integrity is maintained

10.2 Data Extension

• Data stored in a database at a particular time is called Extension

10.3 Important Computer Facts

• Walt Disney acquired Rupert Murdoch's 21st Century Fox's entertainment assets for 71 billion dollars on 20 March 2019
• These include Fox Film and TV Studio, FX Network, National Geographic, Star India, Deadpool, etc.

11. Important One-Liners - Computer Science for SSC CGL

1. CPU = Brain of Computer (Central Processing Unit)
2. Three main components of CPU: ALU, Control Unit, Memory Unit (Registers)
3. Wetware = Human Brain (biological computer)
4. Emulator = program to copy function of one system on another
5. CPU Scheduler = also known as Short-Term Scheduler
6. Computer generations: 1st = Vacuum Tubes; 2nd = Transistors; 3rd = IC (Integrated Circuit); 4th = Microprocessors
7. Third Generation (1965-1975): IC invented by Jack Kilby of Texas Instruments
8. Cache Memory = high-speed semiconductor memory; works between CPU and RAM
9. Cache Memory works on principle of Reference
10. Write-Back = method of updating main memory when word removed from cache
11. Flip-Flop = circuit used for storage of one bit data
12. Page Fault = when program reaches a page not in main memory
13. C language developed by Dennis Ritchie at Bell Telephone Laboratory in 1972
14. UNIX = first operating system written in high-level language (C Language)
15. Linux = Open Source OS; Windows = Microsoft's Commercial OS
16. Query Language = database programming language for searching and retrieving
17. Primary Key is also a Candidate Key
18. Spawn technique used for self-replication of computer virus
19. Daemon = continuously active background system program
20. Opera is a Web Browser (NOT an operating system)
21. HTTP = HyperText Transfer Protocol = Application Protocol; invented by Ted Nelson in 1965
22. UDP = User Datagram Protocol = Connectionless Protocol; designed by David P. Reed
23. Optical Fiber transmits signals by Total Internal Reflection
24. Optical fiber proposed by Charles Kao and George Hockham in 1966
25. Network Congestion = excessive data overloads network
26. Repeater = Physical Layer; Router = Network Layer
27. Token = brief message going from one station to another in network
28. Multicast = sending frame to a group of stations
29. Cloud Computing = computation, storage, application as network service
30. Maximum internet users: China
31. IMPS = Immediate Payment Service; started 22 November 2010; by NPCI
32. ATM = Automated Teller Machine
33. IC = Integrated Circuit (also called Microchip)
34. WIMAX = Worldwide Interoperability for Microwave Access
35. Data Integrity = data in database is correct and consistently complete
36. RAM = Random Access Memory; volatile (data lost when power off)
37. Routing Algorithm = decides path for packet transfer (Source → Destination)
38. Micro-Operation = operations performed on data stored in registers
39. Associative Memory = Content Addressable Memory
40. Garbage Collection = automatic memory management technique