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

NETWORKING

1- Characteristics of Electronic Cables

Impedance, attenuation, and capacitance are crucial in electronic cables.

Impedance:

Resistance to electron movement in an AC circuit, measured in ohms (Ω).

Attenuation:

Resistance to electron flow, measured in db/m.

Capacitance:

Energy storage in a cable, measured in picofarads (pF).

2- Physical Description of Cables

Twisted Pair: Protects against crosstalk and noise.

Coaxial Cable: Consists of copper conductor, plastic insulation, and shielding.

Fiber-Optic Cable: Core, cladding, buffer, strengthening material, and outer jacket.

3- UTP vs. STP

Shielding reduces electrical noise in STP but makes installation complex.

4- Crimping RJ-45 UTP Cables

Creates straight-through and crossover cables for connecting... Continue reading "Understanding Networking: Cables, Protocols, and Topologies" »

Java Programming Fundamentals

This document provides a quick reference to fundamental Java programming concepts, including object-oriented programming basics, common data structures like ArrayLists, handling user input, string manipulation, type conversion, and file input/output operations.

Object-Oriented Programming: The Persona Class

Below is a basic definition of a Persona class, illustrating fields and a constructor. In a complete implementation, you would also include getter and setter methods for each field.

public class Persona {
    private String nombre;
    private int ojos;
    private int piernas; // Added for completeness based on constructor
    private int brazos; // Added for completeness based on constructor

    public Persona(

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Athens Dublin Istanbul Lisbon London Oslo Paris... Continue reading "Customer Feedback and Catalog Request Form" »

Functions and Arguments

A function is a module of program code that takes input (arguments) and produces output (a return value).

• Arguments allow us to customize the operation performed by the function.
• The return value is often the result of executing the code.
• Calling a function causes the code in a function to execute. If called again, it will execute again.

To document a function, use a multi-line comment immediately after the def line.

Local Variables

Local variables are variables used inside functions.

• They are accessible/usable within that function only.
• This refers to the variable's scope.

Global Variables

Global variables are variables used outside of a function.

• Global variables' scope includes both inside and outside of functions.
• However, since

Understanding Computer Security

Common Threats

• Worm: Designed to replicate itself, a worm operates as a standalone application, unlike a virus.
• Trojan: Disguised as a legitimate program (e.g., a screensaver), a Trojan operates covertly to inflict damage.
• Phishing: Attackers impersonate trustworthy entities to steal sensitive information, exploiting social engineering tactics.

Network and Security Concepts

• Simple Mail Transfer Protocol (SMTP): A standard for email communication, SMTP is known for its lack of robust security.
• Sandboxes: Software environments that isolate programs to prevent them from harming the host system, commonly used in web browsers.

Wireless Security

• Wireless Internet (Wi-Fi): Enables wireless communication between devices, forming

Network Classification by Device Roles

Networks can be classified based on the roles of the devices within them:

• Client-Server: This is the most common type. A powerful server provides services to multiple clients and is always available. Example: A web server.
• Peer-to-Peer: In this model, all computers have equal roles and share resources directly. Example: BitTorrent.

Router Functions in Home Networks

Routers provided by Internet Service Providers (ISPs) often integrate the functions of multiple devices, including:

• Hub
• Modem
• Access Point

MAC Address Translation

The MAC address 08-2E-5F-14-93-A0 in decimal is 8-46-95-20-147-160.

Switches and the OSI Model

Switches operate at Level 2 (Data Link Layer) of the OSI model. Other devices that work at this level... Continue reading "Network Types, MAC Addresses, and OSI Model Explained" »

What is a Process?

A process is a program in execution, encompassing the current values of the program counter, registers, and variables. It's an active entity with a limited lifespan, created at execution start and terminated upon completion. Processes utilize various resources like memory, disk, and printers as needed.

Process vs. Program

Multiprogramming and the Process Model

Multiprogramming involves rapidly switching the CPU between multiple... Continue reading "Processes, Threads, and RAID Levels in Operating Systems" »

C-Style Arrays

In stack: int a[3] = {0, 1, 2};

In heap: int* b = new int[3];

Sorting

std::sort(myvector.begin(), myvector.end());

Example 2: std::sort(myvector.begin(), myvector.end(), myCompFunction);

mylist.sort() or mylist.sort(compare_nocase);

bool compare_nocase(const std::string& first, const std::string& second) { return first < second; }

Templated Classes

Include template <typename T> above the header.

Each function has a template declaration:

template <typename T>
class_name<T>::getmax () {
  // ...
}

typedef list_iterator iterator;

Strings

str.substr(3, 5) (starts at position 3, length 5)

str1.compare(str2) != 0

str.length()

Lists

iterator insert(iterator position, const value_type& val); (returns pair)

Maps

std::map&

Telephone Means and Equipment

Fixed individual devices (copper networks have been replaced by optical fiber networks)

Private branch exchanges (PBX): it connects calls between two destinations or ends

Function: call transfers among extensions, caller ID…

Types: IP PBXs call centers, they manage just phone calls contact centres, they not only manage phone calls but emails, SMS, online messages, faxes, etc.

Mobile devices: PDA, Smartphone

Services: Internet, e-mail, videoconference, digital camera, audio an Video quality player, an agenda, GPS, own, Operating system

Additional services offered by the telephone equipment

Common features

A.Fixed telephony: -Notice of charge(aviso de cargo) you receive info on the cost of a call Call forwarding(desvio

Binary Operations and Number Systems

Bitwise Shift Operations

Left Shift

The left shift operator (<<) shifts bits to the left, filling the vacated positions on the right with zeros. This is equivalent to multiplying the number by powers of two.

Right Shift

The right shift operator (>>) shifts bits to the right. There are two types:

• Logical Right Shift: Fills the vacated positions on the left with zeros.
• Arithmetic Right Shift: Fills the vacated positions on the left with the most significant bit (sign bit) of the original number, preserving the sign for signed integers.

Decimal to Binary Conversion

To convert a decimal number to binary, repeatedly divide the decimal number by 2. Record the remainder (which will be either 0 or 1) from right... Continue reading "Essential Computer Science: Binary, OS Kernel, Von Neumann, Assembly" »