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

Essential Linux Commands

File and Directory Management

• mkdir: Create a new directory.
• ls: List contents of a directory.
• rm: Remove files or directories (-r for recursive).
• cp: Copy files or directories.
• mv: Move or rename files or directories.
• cat: Display file contents or create files.
• less: View file contents one page at a time.
• head: Display the first 10 lines of a file.
• tail: Display the last 10 lines of a file.

System Information

• uname: Show system information (kernel, version, etc.).
• top: Display running processes and resource usage.
• df: Show disk space usage.
• df -h: Show disk usage in human-readable format.
• free: Display memory usage (RAM and swap).

File Creation and Editing

• touch: Create an empty file or update its timestamp.
• echo: Write text to a file

1. TCP Congestion Control

Slow Start: TCP initializes congestion window (cwnd) to a small size and doubles it every Round Trip Time (RTT) until a loss occurs (exponential growth) or the slow start threshold is reached.

Congestion Avoidance: After reaching the threshold, cwnd is incremented by one segment for each RTT, growing linearly to avoid congestion.

Fast Recovery: When triple duplicate ACKs are detected, TCP halves the cwnd and reduces the slow start threshold to half of the cwnd size before the loss, then transitions to congestion avoidance.

2. TCP RTT and Timeout

Estimating RTT: Uses Smoothed Round Trip Time (SRTT) which is a weighted average of previous RTT measurements.

Timeout Calculation: Often calculated as Timeout=SRTT+4×RTT

Understanding Linux File Management Subsystem

The Linux File Management Subsystem, an integral part of the Linux kernel and user space, meticulously handles all aspects related to files. This includes their creation, storage, retrieval, permissions, and overall structure. Its primary role is to ensure that data is stored efficiently and securely on disk, remaining readily accessible whenever needed.

Core Components of Linux File Management

File System Interface

• Provides system calls such as open(), read(), write(), and close(), which user programs utilize to interact with files.
• Abstracts the underlying complexity of physical storage devices.

Virtual File System (VFS)

• Acts as a crucial abstraction layer, offering a common interface to various file

Network Switches

Managed vs. Unmanaged Switches

Managed Switch: Configurable via software, supports security and communication settings. Used in large networks (enterprise, universities).

Unmanaged Switch: Fixed configuration, hardware-only, cannot be configured.

Ethernet & Speed

1. Fast Ethernet: 100 Mbps.
2. Gigabit Ethernet: 1 Gbps.

Ethernet Protocol

Divides data into frames, encapsulates IP addresses, performs error detection.

Ports

3. Console Port: Connects PC/laptop to configure switch.

Communication Modes

• Simplex (Half Duplex): One-way communication at a time.
• Duplex (Full Duplex): Two-way communication simultaneously.

Bandwidth

5. Maximum transmission speed of a network, determined by signal frequency range.

IP Addressing & Subnets

6. IP Address: Identifies

Circle Generating Algorithms

Circle generating algorithms are fundamental in computer graphics for rendering circles efficiently on raster displays. These algorithms calculate the points on the circumference of a circle and plot them. The most commonly used circle generating algorithms are the Midpoint Circle Algorithm and Bresenham's Circle Algorithm.

Midpoint Circle Algorithm Steps

The following steps outline the basic process for generating points in one octant, which are then mirrored to complete the circle:

1. Step 1: Initialization. Set starting coordinates $x = 0$ and $y = r$ (radius). Calculate the initial decision parameter $p = 1 - r$.
2. Step 2: Iteration. Repeat the following steps while $x \le y$:
   • Plot the current point $(x, y)$ and its octant

Kerberos: Secure Network Authentication Protocol

Kerberos is a network authentication protocol that allows systems and users to prove their identity to each other before accessing resources, ensuring secure communication within a network. It is a trusted third-party system that verifies user identities without sending passwords directly across the network.

Key Components and Characteristics of Kerberos

Authentication Protocol Definition

Kerberos is a protocol, meaning it is a set of rules and procedures that govern how devices and users authenticate with each other.

Trusted Third Party (KDC)

Kerberos relies on a trusted third party, known as the Key Distribution Center (KDC), to manage authentication.

Single Sign-On (SSO) Implementation

Kerberos is... Continue reading "Kerberos Protocol Authentication and Network Transmission Media Types" »

Internet Fundamentals: A Network of Networks

The Internet is often described as a "network of networks," comprising interconnected Internet Service Providers (ISPs).

Key Components of the Internet

• Hosts: End Systems for Applications

  Hosts are the end systems (clients & servers) that run applications. They connect at the edge of the Internet.

• Packet Switches: Forwarding Data

  Packet switches forward data in chunks called packets. These include:

  • Routers: Forward data between different networks.
  • Switches: Operate within the core of the Internet, not at the edge.

• Communication Links: The Data Pathways

  Communication links connect routers and can be made of:

  • Fiber optic cables
  • Copper wires
  • Radio waves
  • Satellite connections

  The transmission rate of a link is

Types of Interrupts in the 8086 Microprocessor

The 8086 microprocessor utilizes various mechanisms to handle external events and internal errors. These mechanisms are categorized into three primary types of interrupts: Hardware, Software, and Internal (Exceptions).

1. Hardware Interrupts

Hardware interrupts are generated by external hardware devices to request service from the microprocessor. The 8086 supports two hardware interrupt pins:

• INTR (Interrupt Request)

  This is a maskable interrupt, meaning it can be enabled or disabled using the IF (Interrupt Flag) in the flag register. When an external device wants to interrupt the microprocessor, it sends a signal on the INTR pin.

  The 8086 acknowledges the interrupt if the IF flag is set, and the INTA

Windows Popularity and Vista Features

Unit 13

Interviewer: There is no doubt that Windows has revolutionized the way we use computers today. Bill, can you explain just why it’s so popular?

Bill: Well, very simply, people find Windows very easy to use because everything is presented in graphic images. It’s also compatible with thousands of programs.

Interviewer: The big news at the moment is, of course, the launch of Windows Vista – the successor to Windows XP. I understand that there are several versions of Vista available. Could you give us some advice on which one to get?

Bill: Yes, you’re right – there are four main editions: Home Basic, Home Premium, Business and Ultimate.

Windows Vista Editions:

• Home Basic: Designed for users with basic