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

Certainly! Here is a cheat sheet for computer architecture:

1. Central Processing Unit (CPU)

• The "brain" of the computer that executes instructions.
• Consists of the Control Unit (CU) and the Arithmetic Logic Unit (ALU).
• Fetches instructions from memory, decodes them, and executes them.

2. Memory Hierarchy

• Registers: Fastest and smallest storage units located within the CPU.
• Cache: High-speed memory that stores frequently accessed data.
• Main Memory (RAM): Larger storage used to hold data and instructions.
• Secondary Storage: Non-volatile storage devices like hard drives and SSDs.

3. Instruction Cycle

• Fetch: The CPU fetches the next instruction from memory.
• Decode: The instruction is decoded to determine the operation.
• Execute: The instruction is executed

Building a Sudoku Solver in Java with Backtracking

This document presents a Java implementation of a Sudoku solver, utilizing a classic backtracking algorithm. The code demonstrates how to represent a Sudoku board, check for valid moves, and recursively find a solution to the puzzle.

Initial Sudoku Puzzle Setup

The Sudoku board is represented as a 2D integer array. A value of 0 indicates an empty cell that needs to be filled.

int[][] board = {
  { 8, 0, 0, 0, 0, 0, 0, 0, 0 },
  { 0, 0, 3, 6, 0, 0, 0, 0, 0 },
  { 0, 7, 0, 0, 9, 0, 2, 0, 0 },
  { 0, 5, 0, 0, 0, 7, 0, 0, 0 },
  { 0, 0, 0, 0, 4, 5, 7, 0, 0 },
  { 0, 0, 0, 1, 0, 0, 0, 3, 0 },
  { 0, 0, 1, 0, 0, 0, 0, 6, 8 },
  { 0, 0, 8, 5, 0, 0, 0, 1, 0 },
  { 0, 9, 0, 0, 0, 0, 4, 0, 0 }
};

Implementing

Packet Fragmentation: Layer 3 vs. Layer 2

As mentioned in the “Link-Layer Fragmentation and Interleaving” section, PPP, Frame Relay, ATM, and other WAN technologies support fragmenting packets (frames) at Layer 2. As you may have learned in basic networking classes, IP can also fragment packets at Layer 3. What are some advantages and disadvantages of fragmenting at Layer 3 versus fragmenting at Layer 2?

Advantages and Disadvantages

• Advantages (Layer 3 Fragmentation): Large packets can be transmitted at Layer 2 as fragmentation is done at Layer 3. This reduces the number of acknowledgment exchanges. Also, maintaining the order of fragments to ensure the order of transmission and reassembly is not required.
• Disadvantages (Layer 3 Fragmentation)

Chapter 1 Introduction to Services

3.1. Service Terminology Service

a service is a software program that makes its functionality available via a technical interface, called a service contract.

Figure 3.1. The symbol used to represent an abstract service.

Service Contract

The symbol used to represent a service contract is displayed in Figure 3.2.

Service Capability

A service contract can be broken down into a set of service capabilities, each of which expresses a function offered by the service to other software programs.

Figure 3.4. A Purchase Order service contract with four service capabilities.

Service Consumer

A service consumer is software program when it accesses and invokes a service—or, when it sends a message to a service capability

Service

1. Visibility of System Status

The system should always keep users informed about what is going on, through appropriate feedback within a reasonable time.

2. Match Between System and the Real World

The system should speak the user's language, with words, phrases, and concepts familiar to the user, rather than system-oriented terms. Follow real-world conventions, making information appear in a natural and logical order.

3. User Control and Freedom

Users often choose system functions by mistake and will need a clearly marked "emergency exit" to leave the unwanted state without having to go through an extended dialogue. Support undo and redo.

4. Consistency and Standards

Users should not have to wonder whether different words, situations, or actions... Continue reading "10 Usability Heuristics for User Interface Design" »

Problem Statement

Explore the usage of basic Linux system calls.

Process Management System Calls

The system calls to manage processes are:

• fork(): Used to create a new process.
• exec(): Executes a new program.
• wait(): Waits until the process finishes execution.
• exit(): Exits from the process.

System calls used to get process IDs are:

• getpid(): Gets the unique process ID of the process.
• getppid(): Gets the parent process's unique ID.

Stat System Call

The stat system call retrieves information about files, specifically from their inodes. For instance, to get a file's size and name, you would typically use stat. Let's illustrate with a C code snippet (src/ls1.c):

#include<stdio.h>
#include<dirent.h>
#include<cstdlib>

struct dirent *dptr;

Java Membership Dues Calculator Example

Below is a corrected and formatted Java example that demonstrates conditionals, a switch, and loops. All original content has been preserved and corrected for spelling, grammar, and capitalization.

import java.util.Scanner;

public class DuesCalculator {
    public static void main(String[] args) {
        // TODO: application logic here
        // 1
        char standing;
        double gpa = 0, dues = 0;
        // 2
        Scanner keyboard = new Scanner(System.in); // import java.util.Scanner

        System.out.print("Enter your class standing: ");
        standing = keyboard.nextLine().charAt(0);

        System.out.println("Enter your GPA:");
        gpa = keyboard.nextDouble();

        // System.

WEEK 1: Software that Manages Computer Hardware

Operating System as an Abstract Machine, Service Provider, and Resource Manager. OS Objectives: Convenience, Efficiency, and Ability to Evolve.

Performance Indices

Arrival Time, Service Time, Turnaround Time, Normalized Turnaround Time. First-Come-First-Served (FCFS) Scheduling Policy.

Microprocessor and DMA Activity

Impact of Microprocessor Bus Configuration and DMA Activity on System Speed.

Memory System and Cache

Cache and Main Memory Access Time, Average Access Time Calculation.

iOS and Android

Similarities and Differences between iOS and Android.

Job Execution and CPU Utilization

CPU Utilization for Uniprogramming and Multiprogramming.

Direct Memory Access (DMA)

Coordination, Memory Operations Completion,... Continue reading "Understanding Operating Systems: Functions, Performance, and Multithreading" »