Notes, summaries, assignments, exams, and problems for Computer science

PC Hardware: Essential Components

Hardware refers to the set of physical elements, machinery, and components (such as the microprocessor, monitor, and keyboard) that constitute a personal computer (PC).

Software, on the other hand, consists of programs or applications, along with the data or information they process and store.

Understanding Data and Information

Data serves as the raw material input that computers transform into information. Processed data, or information, is the result, distinguished by its usefulness.

Key Characteristics of Useful Information:

• Relevant: The information is applicable to the current situation.
• Current: Information is updated and available precisely when needed.
• Accurate: Data entered into a computer and the resulting

Memory Management Definition

Memory management is the process of:

• Bringing programs into the main memory to be executed by the processor.
• Dynamically dividing the part of main memory to accommodate multiple processes.
• Allocating memory efficiently for packaging processes, preventing the processor from being idle.
• Enabling the execution of a larger program than is available in real memory.

Memory Management Requirements

1. Relocation

• Ability to move a program from one region to another of the main memory without invalidating the memory references.
• The processor hardware and operating system translate the memory references' addresses to the final physical memory addresses.

2. Protection

Each process must be protected from unwanted interference from other...

Operating System Fundamentals

CPU Scheduling Algorithms

CPU scheduling algorithms determine the order in which processes are executed by the CPU. Each algorithm has distinct characteristics and trade-offs.

First-In, First-Out (FIFO)

This scheduling algorithm processes tasks in the order they arrive. While simple, its main disadvantage lies in potential performance bottlenecks, as a long process can block shorter ones, leading to inefficient CPU utilization.

Shortest Remaining Time (SRT)

A preemptive version of Shortest Job First (SJF). If a new process arrives with a shorter remaining execution time than the currently running process, the CPU switches to the new, shorter process. This aims to minimize average waiting time.

Shortest Job First (SJF)

Understanding Firewalls

A firewall is a point between two or more networks, acting as a component or set of components through which all traffic passes. It enables the control, authentication, and logging of all network traffic.

Note: A firewall does not authenticate or protect data from viruses.

Key Features

• Packet Filter: Performs selective packet routing by analyzing data from headers.
• Proxies: Analyzes packets at the application layer.
• Bastion Hosts: Dedicated equipment with minimal services installed, kept at the latest version, to offer services to the internet.

Network Address Translation (NAT)

• Converts invalid or reserved IP addresses into valid, routable addresses.
• Solves the shortage of valid IP addresses.
• Provides masking for the internal

CARLOS HAYA IES Building Computer Room Web pages pag. 3

Website Structure Types

The basic structures we observe at any site are one of the following types:

Tree Structure

In this structure, there is a main page (the home page in English terminology) from which you can reach other sites on the Web. In this way, the pages come to be grouped into levels, so that to get from the first to the last, you must pass through the middle. It is a very hierarchical structure and can be difficult to navigate if levels are excessive.

This structure may be ideal for a site organized in groups of separate pages.

In any case, the number of levels should not be excessive, never more than 3.

List Structure

There is no home page; what we have is a sort of list of pages...

Understanding Websites and HTML

A website is a document written in HTML (HyperText Markup Language). It is a system that allows us to format text using tags. A web page can be composed of images, sounds, videos, and animations. HTML is a language focused on the transmission of documents using the HTTP protocol.

A website is a collection of pages linked together. These are viewed through programs called browsers, which interpret the tags added to the text, such as:

• Mozilla Firefox
• Google Chrome
• Opera

HTML uses two types of labels: opening (<tag>) and closing (</tag>). A website consists of a header and a body. Common tags include:

• Header: <h1>
• Paragraph: <p>
• Bold: <b>
• Italic: <i>
• Underlined: <u>
• Horizontal Line:

System Recovery and Troubleshooting

When repairing an Operating System (OS), specifically Windows XP, there are two primary options available:

• Emergency Repair Disk (ERD): Known previously as DRE.
• Restore Points (RP): System backups performed automatically.

Windows XP Recovery Methods

The original Floppy-based Emergency Repair Disk action that existed in older versions of Windows was deleted in Windows XP. This change occurred because modern computers support booting from the CD-ROM drive. The ERD functionality was replaced by a mixed, recoverable method, often utilizing a diskette as a storage medium.

Restore Points: These are backups performed automatically at regular intervals. They allow you to recover a damaged system state by reverting to a...

Network Communication Methods: Switching Techniques

Circuit Switching

Allows two terminals to communicate through a single, dedicated circuit, leaving it free for use during the connection.

Benefits of Circuit Switching

• Real-time transmission.
• No interference from other users on the loop.
• No contention or congestion issues.
• No time is lost in recalculating routes.
• Simplicity in management.

Disadvantages of Circuit Switching

• Initial connection delay.
• Time is wasted when the circuit is idle.
• Route recalculation does not inherently lower costs.
• Low fault tolerance.

Message Switching

The full message is sent to a node, which stores and forwards it to the next node until it reaches its destination.

Benefits of Message Switching

• The channel is released before the

The scanner is a computer input device that allows you to scan images or documents using Optical Character Recognition (OCR). It emits light onto the document being scanned and captures the reflected light using a photosensor.

Types of Software

• OCR (Optical Character Recognition): Software specializing in extracting text characters from scanned document images, converting them into editable text.
• OMR (Optical Mark Recognition): Software designed to extract marks from documents, storing them as database fields.

Transmission of Photographs

• Wired: Traditional cable connections.
• Card Reader: For transferring data from memory cards.
• Infrared: Transmits and receives waves in the infrared spectrum. Requires devices to be side-by-side for communication (2-

What is DNS?

DNS (Domain Name System) is a service responsible for translating IP addresses into domain names and vice versa. It follows a client-server architecture and consists of a massive distributed database managed by specialized software.

Hierarchical Structure of DNS

• Root DNS Server: There are 13 super-servers scattered globally that work in unison. They contain the master tables for name resolution, though most operational work is delegated to other servers.
• Top-Level Domains (TLD): Maintained by internet authorities, these resolve top-level domain names.
• Second-Level Domains: These resolve second-level domain names and are maintained by domain owners or Internet Service Providers (ISPs).
• Subdomains: Added to the left of the domain name,