Notes, summaries, assignments, exams, and problems for Computers

What is Information Security?

Information security means protecting data from theft, alteration, destruction, disclosure, or denial of access. It has traditionally relied on physical measures (e.g., locked cabinets) and administrative controls (e.g., personnel screening). Even today, some reliance on physical security remains.

Modern Information Security Needs

With increased computer usage, automated tools are now essential for protecting stored information. As network usage grows, securing data during transmission has become equally essential.

Aspects of Information Security (ITU-T X.800/1205)

• Security Attack: Any action that compromises system security.
• Threat: A potential violation, defined as capability plus intent.
• Security Mechanism: Any policy

IoT Protocols

Link Layer Protocols

• 802.3 Ethernet Standards

  A collection of wired Ethernet standards that provide data rates from 10 Mb/s to 40 gigabits per second. The shared medium in Ethernet can be a coaxial cable, twisted-pair wire, or optical fiber. This shared medium carries communication for all devices on the network.

• 802.11 Wi-Fi Standards

  A collection of wireless Local Area Network (WLAN) communication standards.

Network/Internet Layer

• Responsible for sending IP datagrams from the source network to the destination network.
• Handles host addressing and packet routing based on IPv4 or IPv6.
• Datagrams contain a source and destination address, which are used to route them from the source to the destination across multiple networks.
• IPv4 uses 32-

Express.js Routing Basics

The first example sets up a simple Express.js server with static routes, a dynamic route, and a 404 handler.

const express = require('express');
const app = express();

// Route 1
app.get('/', (req, res) => {
  res.send('Home Page');
});

// Route 2
app.get('/about', (req, res) => {
  res.send('About Page');
});

// Route 3: Dynamic route
app.get('/users/:id', (req, res) => {
  res.send(`User ID: ${req.params.id}`);
});

// 404 handler: Keep it last
app.use((req, res) => {
  res.status(404).send('404 - Page Not Found');
});

app.listen(3000, () => {
  console.log('Server running on port 3000');
});

Building a RESTful Student API

The second example implements a RESTful API for managing students, supporting... Continue reading "Express.js Routing and CRUD API for Student Management" »

1. Functional Dependency (FD)

A functional dependency A → B means: if you know the value of attribute A, you can always determine the value of attribute B. In other words, no two rows can have the same A value but different B values.

Example: In a table Student(StudentID, Name, Email): StudentID → Name, Email (Given a StudentID, the Name and Email are always uniquely determined.)

2. Boyce-Codd Normal Form (BCNF)

A relation is in BCNF if, for every functional dependency X → Y, X is a superkey.

• Compliance: Every determinant in the table is a candidate key—no changes needed.
• Evaluation: Whenever there is a non-trivial FD X → Y where X is not a superkey. This means some attribute depends on only part of a key, or on a non-key attribute—causing

1. Compare text files and binary files with respect to storage, processing speed, memory utilization, and applications.

Comparison Between Text Files and Binary Files

Real-Time Operating System (RTOS)

A Real-Time Operating System (RTOS) is an operating system that provides a response within a specified time limit. It is used in applications where timing is critical.

Types of RTOS

• Hard Real-Time OS: The deadline must be met. Missing a deadline may lead to system failure.
• Soft Real-Time OS: Occasional delays are acceptable, but performance may be affected.

Applications of RTOS

• Medical Equipment
• Robotics
• Air Traffic Control Systems
• Industrial Automation
• Automobile Control Systems

Advantages of RTOS

• Fast response
• High reliability
• Predictable performance

Critical Section

A Critical Section is the part of a program where a process accesses or modifies shared data or resources. Only one process should execute its critical section... Continue reading "OS Concepts: RTOS, Critical Section, Memory & Deadlocks" »

Java Programming Fundamentals and Features

Java is a high-level, object-oriented, platform-independent programming language developed by Sun Microsystems (now owned by Oracle) in 1995. Java follows the principle "Write Once, Run Anywhere (WORA)", meaning a Java program can run on any system that has a Java Virtual Machine (JVM).

Key Features of Java

• Simple: Easy to learn and use.
• Object-Oriented: Based on the concept of classes and objects.
• Platform Independent: Runs on any operating system using the JVM.
• Portable: Programs can be moved easily from one platform to another.
• Secure: Provides security through bytecode verification and the JVM.
• Robust: Features strong memory management and exception handling.
• Multithreaded: Supports the execution of multiple

Subroutines and Control Instructions

A subroutine is a group of instructions written to perform a specific task. It can be called from different parts of a program using the CALL instruction, and after execution, it returns to the main program using the RET instruction.

Example:

CALL 2500H ; Call subroutine at address 2500H

2500H: INR A ; Increment accumulator

RET ; Return to main program

• CALL 2500H transfers control to address 2500H.
• The instructions at 2500H are executed.
• RET returns control to the instruction immediately after CALL.

Unconditional Jump (JMP)

Example: JMP 3000H (Assembly Language)

• The CPU immediately jumps to memory address 3000H.
• Execution continues from 3000H.
• No flag (Zero, Carry, Sign, etc.) is checked.

Interrupts and Control Signals

RST

Border Gateway Protocol (BGP)

BGP (Border Gateway Protocol) is a routing protocol used to exchange routing information between different networks or Autonomous Systems (AS) on the Internet. It is called an inter-domain routing protocol because it works between different networks.

Roles of BGP

• Connects different Autonomous Systems.
• Exchanges routing information between networks.
• Selects the best path for data transmission.
• Prevents routing loops.
• Maintains internet routing tables.

Example: When a user using Airtel internet accesses a Google server, BGP helps choose the best route between the Airtel network and the Google network.

CSMA/CD: Collision Detection in Ethernet

CSMA/CD stands for Carrier Sense Multiple Access with Collision Detection. It is a... Continue reading "Essential Computer Networking Protocols and Mechanisms" »