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

1. Boot Sector Virus

• It is a type of virus which infects the master boot record (portion of the hard disk which helps to load the OS) or hard disks.
• The infected code runs when the system is booted from an infected disk.
• They infect at a BIOS level (BIOS checks hardware and loads the OS).
• They use DOS commands (text-based commands used to perform tasks such as file management, disk management, and running programs) to spread to other floppy disks. Since floppy disks are rarely used now, the propagation of boot sector viruses has almost ended.
• With the boot-sector safeguards in operating systems, boot-sector viruses can no longer infect computers.
• This virus can infect a computer only during boot-up. Once the system has started and the OS is running,

Compile and Go Loaders

In this type of loader, the linker and loader instructions are read line by line, their machine code is obtained, and it is directly placed in the main memory at some known address. This means the assembler runs in one part of memory, and the assembled machine instructions and data are directly put into their assigned memory locations. After completion of the assembly process, the loader contains the instruction using which the location counter is set to the start of the newly assembled program. A typical example is WATFOR-77, a FORTRAN compiler which uses such a "load-and-go" scheme. This loading scheme is also called "assemble-and-go".

Advantages

• Simplicity
• Quick Testing
• No Separate Linking
• Immediate Feedback
• Low Resource

What is an Exception?

Answer: An exception in Python is an error that occurs during program execution, disrupting the normal flow of instructions. Instead of crashing, the program can "catch" the exception and handle it gracefully using try and except blocks. Common exceptions include ZeroDivisionError, IndexError, and FileNotFoundError. You can also define custom exceptions. The finally block can be used for cleanup actions, ensuring certain code runs regardless of whether an exception was raised.

Different Modes of Opening a File

Answer: Different Modes of Opening a File

1. Read Mode ('r')

• Purpose: Opens a file for reading.
• Behavior:
  • The file pointer is placed at the beginning of the file.
  • If the file does not exist, a FileNotFoundError is raised.

Definition of Software Engineering

Software engineering is the establishment and use of sound engineering principles in order to obtain software economically that is reliable and works efficiently on real machines.

Need for Software Requirements Specification (SRS)

The Software Requirements Specification (SRS) is necessary because it provides:

• A detailed overview of the software product, including its parameters and goals.
• A description of the project's target audience, user interface, and hardware and software requirements.
• A common understanding of how the client, development team, and audience perceive the product and its functionality.

Four Core Principles of Software Engineering

1. The Reason It All Exists (Value to Users)

• A software system exists

Master-Slave Flip-Flop Operation

The working of a Master-Slave flip-flop involves two cascaded flip-flops: a master and a slave. The master is positive level-triggered, and the slave is negative level-triggered, ensuring the master responds before the slave.

When the clock pulse (CP) goes high (1), the slave is isolated, allowing the J and K inputs to affect the master's state. The slave flip-flop remains isolated until the CP goes low (0). When the CP transitions back to low, information is passed from the master flip-flop to the slave, and the output is obtained.

Let's examine the behavior based on J and K inputs:

• J=0, K=1: The high Q' output of the master goes to the K input of the slave. The negative transition of the clock forces the slave

C Programming Examples

Here are several C programming examples:

Vector Operations

#include <stdio.h>

void leVetor (int v [] , int tam );
int prodEscalar (int v1 [] , int v2 [] , int tam );

int main (void) {
    int v1 [ DIM ], int v2 [ DIM ];
    int i;
    int prod ;

    leVetor (v1 , DIM );
    leVetor (v2 , DIM );
    prod = prodEscalar (v1 , v2 , DIM );
    printf ("%d\n", prod );
    return 0;
}

void leVetor (int v [] , int tam ) {
    /* Completar */
}

int prodEscalar (int v1 [] , int v2 [] , int tam ) {
    /* Completar */
}

Random Number Generation

#include <stdio.h>
#include <time.h>
#include <stdlib.h>

#define VEZES 10

int main (void) {
    int i , j , k;
    double r;

    srand ( time ( NULL )); /* inicializa

Heuristic Search Techniques Explained

Heuristic search techniques use intelligent estimations to find solutions efficiently. These methods help in decision-making by prioritizing the most promising paths.

1. Greedy Best-First Search (GBFS)

• Always chooses the next step that appears closest to the goal.
• Ignores the cost already traveled.

Example:

A person finding the exit of a maze by always taking the path that looks shortest.

⚠ Risk: May lead to dead ends.

2. A* Search Algorithm

• Balances actual cost and estimated cost to reach the goal.
• Ensures the shortest and most efficient path.

Example:

Google Maps finds the best route by considering both distance already covered and the remaining estimated distance.

✅ Optimal and efficient.

3. Hill Climbing Algorithm

• Moves

Sequential circuits are fundamental components of digital systems, defined by the fact that their output depends not only on the current inputs but also on the past history of inputs (i.E., their current state).
The most basic element of a sequential circuit is the Flip-Flop, which is a 1-bit memory cell.
Here is a detailed explanation of the basic Flip-Flops and their operation:
1. Latches vs. Flip-Flops
Both latches and flip-flops are 1-bit storage elements, but they differ in how they are controlled:
| Feature | Latch | Flip-Flop |
|---|---|---|
| Triggering | Level-triggered (Transparent) | Edge-triggered (Synchronous) |
| Control | Changes state as long as the Enable or Clock is HIGH (or LOW). | Changes state only at the rising edge or falling... Continue reading "Hehhrhrhr" »

Implementing Boolean Functions with Truth Tables

Problem 1: Implement the following function F(A, B, C) = Σ(2, 5, 6, 7) using a truth table with:

• a. Decoder
• b. Multiplexer

Truth Table for Function F(A, B, C)

a. Decoder Implementation

A decoder is used to select one of the outputs based on the input combination. In this case, we have 3 inputs (A, B, C) and 8 possible combinations. The truth table shows that F = 1 for input combinations (010), (101), (110), and (111), and F = 0 for all other combinations. To implement this, we connect the corresponding decoder outputs to an OR gate.

b. Multiplexer Implementation

A multiplexer (MUX) selects one of the input lines and passes it to the output. The selection is controlled... Continue reading "Implementing Logic Functions with Decoders and MUXs" »