Notes, summaries, assignments, exams, and exercises for Computer science for Secondary education

File Management

File management is the system an operating system uses to organize and keep track of data. The operating system stores data in units called files, determines how files are stored, efficiently uses available storage space, creates a record of all file usage, and carries out every task related to files and folders.

File names typically have this structure:

filename.extension

Task and User Management

Task Management

Task management is the part of the operating system that controls the running of one or more programs on a computer simultaneously. Today's widely used operating systems support multitasking, allowing multiple tasks to run concurrently, taking turns using the computer's resources.

User Management

With user management, the operating...

Understanding Computer Networks

• A computer network is the interconnection of multiple devices, generally termed as hosts, connected using multiple paths for the purpose of receiving data or media.
• Connected devices share information and resources.
• The channel or line is where this information is transmitted.

Computer Network Classifications

Networks can be classified in several ways:

1. By Size: The most common classification.
2. By Property
3. By Connection Method
4. By Topology

1. Network Classification by Size

• LAN (Local Area Network): Maximum of a building. The most frequent type, common in most offices.
• MAN (Metropolitan Area Network): Maximum of a city, connecting different buildings.
• WAN (Wide Area Network): Connects devices from different cities or even countries.

THE WEB:

1. WEB1.0, WEB 2.0, WEB 3.0:

-WEB 1.0 or the read-only web: In the 1990s, information on the Internet was only for reading. It was a network of documents and people could not interact with the content. For example, they couldn’t give their opinions, ask for information or register as users. In addition, the information online was not updated very frequently. Almost everything that people used online was also part of the World Wide Web (www).

WEB 2.0 or the social network:

This was developed during the first decade of the 21st century. In this new web, information became bidirectional. Users could not only receive information, but also create and share it. New services appeared and became popular, such as email, chats, videoconferences,...

Comandos Esenciales de Iptables

• Listar reglas: iptables -t nat -L --line-numbers
• Política por defecto: iptables -t filter -P OUTPUT DROP
• Permitir HTTP e ICMP: iptables -A OUTPUT -o eth0 -p tcp --dport 80 -j ACCEPT
• Permitir Correo (25, 110): iptables -A INPUT -s 0.0.0.0/0 -p tcp --dport 25 -j ACCEPT
• Bloquear PING de IP específica: iptables -A INPUT -o eth0 -s 192.168.28.200 -p icmp -j DROP
• Redirección de puertos (80 a 8080): iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j REDIRECT --to-port 8080
• DNAT (Redirección a IP): iptables -t nat -A PREROUTING -i eth1 -p tcp --dport 80 -j DNAT --to 192.168.10.12:80
• Backup de reglas: iptables-save > mi_tabla y iptables-restore < mi_tabla
• Borrar reglas: iptables -t nat -F y iptables -D INPUT

Behavioral Architecture of a State Machine

This VHDL code describes the behavioral architecture of a state machine.

Network Management Fundamentals

Network management consists of deciding how to configure the network, joining teams, determining what permissions users will have, and handling all tasks related to the operation of the network.

Client/Server Network Architecture

A client/server network consists of the following components:

• Server: Network equipment more powerful than the others, acting as the central controller. The server sets up the network and its policies.
• Client Computers: Devices connected to the server that depend on it for resources and services.
• Shares (Resources): Devices like printers, faxes, and other peripherals used by all network users.
• Connection Devices: Equipment that connects all the computers composing the network (e.g., switches,

Grammar and Phrasing Corrections

Adjective Replacement Example

Original: It is a swan around the house.
Corrected: It is a calm swan.

Grammatical Correction Example

Original: Gradually have damaged the work of humans.
Corrected: They gradually damaged the artwork.

What is a Text?

A text is a group of sentences that constitute a coherent, autonomous, and communicative unit.

Digital Communication Concepts

Chat

An electronic discussion, essentially a conversation conducted over a network.

Email

Email allows users to compose, send, and receive messages via electronic communication systems. Each email message typically has two main components: the header and the body.

Instant Messaging

Instant messaging is a system for exchanging messages between two or more people...

The CSS Box Model Fundamentals

The CSS Box Model is the absolute foundation of web layout and design. In CSS, virtually every HTML element is treated as an invisible, rectangular box. The Box Model is the set of rules that defines how the dimensions, spacing, and borders of these boxes behave and interact with each other.

The Four Layers of the Box Model

Every CSS box consists of four layers, nesting inside one another like Russian nesting dolls. Moving from the innermost layer to the outermost layer:

1. Content

This is the core of the box where your actual content lives—such as text, an image, or a video. Its dimensions are controlled by the width and height properties.

2. Padding (Inside Space)

Padding is the clear space around the content, but...

What is a DBMS?

• DBMS: Software used to store, manage, and retrieve data.
• Acts as a bridge between the user and the database.

Advantages of DBMS

• Reduces data redundancy
• Improves data consistency
• Provides data security
• Enables backup and recovery
• Facilitates data sharing

File System vs. DBMS

• File System: Lower security, higher redundancy.
• DBMS: High security, lower redundancy.

Three-Schema Architecture

1. External Level: User view.
2. Conceptual Level: Logical structure.
3. Internal Level: Physical storage.

Schema and Instance

• Schema: Structure of the database (rarely changes).
• Instance: Actual data at a specific moment (changes frequently).

Data Models

• Hierarchical
• Network
• Relational (most used)
• Object-oriented

Relational Model

• Data stored in tables (relations).

Key Terms

• Tuple:

MEGA CHEAT SHEET

1. Programming Fundamentals

Software Development Life Cycle (SDLC)

Steps: Requirements → Specifications → Design → Development → Integration → Testing/Debugging → Installation → Maintenance.

Mnemonic: Really Smart Developers In Tech Install Machines.

Algorithms

• Control Structures:
  • Sequence (In Order)
  • Selection (If/Else)
  • Iteration (Loops)
• Design Strategies: Divide and Conquer, Backtracking.
• Representations: Pseudocode, Flowcharts, Structure Charts, Abstraction Diagrams.
• Checking: Identify Input/Output, Purpose, Desk Check with data.

Programming Paradigms

• Imperative: Step-by-step instructions (e.g., Python).
• OOP: Objects and classes (e.g., Java, Python).
• Logic: Facts and rules (e.g., Prolog).
• Functional: Pure functions, no state