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

Core Web Technologies Explained

XHTML: Structured Markup

XHTML is HTML based on XML. With it, you can combine HTML markup with XML rules. The idea is to have a standardized document and to be made accessible across multiple platforms and devices, such as a computer desktop, PDA, mobile phone, or TV.

CSS: Appearance Standards

CSS (Cascading Style Sheets) is another important technology. With CSS, you can set standards for the appearance and behavior of page elements. The colors, paragraphs, margins, spacing, thickness, or other page elements can be defined in one file. Therefore, at any time, you can totally change the way all pages of a site look by simply changing the file that contains the CSS definitions. This feature, in conjunction with AJAX,... Continue reading "Mastering Web Technologies: XHTML, CSS, and AJAX Components" »

Operating Systems

What are operating systems? This question can be answered at several levels.

Firstly, an operating system is a program, or a set of programs. Operating systems vary in size from very small to very large, but all are pieces of software. In the past, almost all operating systems were written in a low-level language. Currently, many operating systems are partly or completely written in a high-level language.

Secondly, an operating system is, by virtue of its name, a system. It is a collection of parts working together towards some common goals. The goals or objectives of an operating system may be regarded as the manager of these resources.

Thirdly, a computer may be regarded as a set of devices, or resources, which provide a number... Continue reading "Understanding Operating Systems: Definition and Functions" »

Network Interface Card (NIC)

The Network Interface Card (NIC), also known as a Media Access Unit (MAU), is the device that connects a station (computer or other network device) to the physical network environment. While often presented as an expansion card for computers, many modern computers have integrated network interfaces, primarily Ethernet.

Sometimes, a network card requires a transceiver. This device connects the physical medium to the card, either because a direct connection is impossible (e.g., 10Base5) or because the medium type differs from what the card supports.

Bridge or Bridges

A bridge interconnects two segments of a computer network or divides one network into two segments. It filters data based on the MAC address. Therefore,... Continue reading "Essential Network Hardware Components Explained" »

Network Architectures and Technologies

According to the architecture: Arcnet, Ethernet, Token Ring, FDDI, ATM, ISDN, Frame Relay, DSL, and X.25.

Geographic Extent of Networks

• PAN (Personal Area Network): Home networks covering nearby areas within the same environment, such as the dependencies of a house (living room, bedroom, office, etc.). Example: Home Office.
• LAN (Local Area Network): Covers areas around local area networks within the same environment, such as offices, condominiums, schools, or a university campus.
• MAN (Metropolitan Area Network): Networks covering the metropolitan area of a large city or between nearby cities. Example: Speedy, Virtua.
• WAN (Wide Area Network): Long-distance networks connecting computers located in different cities,

Backup

Important directories: /etc, /home, /var, /usr, /local

Package and compress with tar. Files: home.tar

# tar -cvf home.tar /home

Compression:

# gzip -r /home/* (recursive compression)

Decompression:

# gunzip -r /home/* (recursive decompression)

Cryptography

In cryptography, digital signatures are a digital information authentication method, known as signature.

The art of cryptanalysis is the study of attempts to break ciphertext.

Key + algorithm + message = ciphertext

CID + Authentication + Irretrievability

Encryption: C = Ek(M). Decryption: M = Dk(C)

Steganography: secret communication by hiding the existence of the message.

Steganalysis: detection of steganographic content.

Examples of cryptographic protocols: SSL, SSH, IPSec, WEP, WPA

Symmetric algorithms:... Continue reading "Backup, Cryptography and GnuPG: A Practical Security Reference" »

TCP/IP Protocol Suite Characteristics

• Based on open and free protocols and standards.
• Provides software and hardware independence.
• Uses a common addressing scheme allowing any TCP/IP device to locate another anywhere on the network.
• Includes high-level, standardized protocols supporting widely available and consistent user services.
• Acts as a de facto standard for networking.
• Allows the interconnection of networks with diverse features and technologies.

Internet Protocol Family Fundamentals

The Internet protocol family, commonly known as TCP/IP, is a set of network protocols fundamental to the Internet, enabling data transmission between computer networks. Examples include HTTP, ARP, Telnet, and POP.

Understanding Routers and Their Function

Routers are... Continue reading "Core Networking Concepts: TCP/IP, Routers, and DNS" »

Understanding Wide Area Networks (WANs)

A WAN (Wide Area Network) spans a large geographic area, sometimes a country or continent. It contains a collection of machines dedicated to running user programs. These machines are called Hosts. The hosts are connected by a communication subnet. The subnet's job is to conduct messages from one host to another. The separation of the unique aspects of the communication network (subnet) and areas of application (hosts) greatly simplifies the overall design of the network.

Key Components of a WAN

• Switching Computers (ECD): Each ECD uses a protocol responsible for routing the data correctly and providing support to computers and end-user terminals connected to it.
• Computer User (DTE): The DTE support function

Disney Transport Layer Considerations

The transport layer is the heart of the whole hierarchy of protocols.

Function: To provide efficient, reliable, and economic data transport processes for the application layer, regardless of the physical network or networks.

There are two types of service: connection-oriented and connectionless.

If there is an error in the lower layers, where n can be controlled at higher x, the error is corrected at the transport layer.

• Disorders
• Duplication
• Loss

Causes of errors:

• Cable errors
• Interference
• Inadequate blockade operation

Functions in the Transport Layer

• End-to-end reliable communication
• Error control
• Flow control
• Multiplexing of several connections

Origin and destination communicate through a network. The transport layer... Continue reading "Disney Transport Layer: Understanding Network Communication" »

Biometric Systems: Enhancing Security

Biometric systems, applied to information systems, allow for the authentication of individuals using electronic technologies. These technologies employ complex mathematical formulas to ensure that the person applying for entry to a resource, or a physical space, is who they claim to be.

Increased Security with Biometric Access Systems

Personal identification methods to control access are based on:

• Something you know: passwords or access keywords.
• Something you own: for example, an encoded magnetic card.
• A personal characteristic: such as fingerprints or iris.

Combining two or more methods provides an even higher level of security.

Biometrics: Key Characteristics

• Universality: All individuals possess this characteristic.

Understanding Linux: Kernel, Free Software, and Distributions

Like any operating system, Linux is a combination of a main program, or kernel, and a series of added tools and libraries that enable its use. It possesses two distinguishing features:

• It is free software.
• It is distributed with its source code.

Most programs and libraries added to the Linux kernel to create a more user-friendly system have been developed by the GNU Project. For this reason, some people refer to Linux as GNU/Linux, clarifying that the operating system comprises not only the kernel but also all those programs and libraries.

Key Concepts Defined

Free Software

Software that can be used, copied, studied, modified, and redistributed freely.

Source Code

A set of text lines that