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

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.

Component Architecture

A component diagram illustrates the three layers:

• User layer (interface)
• Login layer (business rules)
• Data layer (database)

The use of interfaces and menus indicates who created the interface design.

Object Fundamentals

Class -> identity + state + behavior

Denormalization: The process of reverting from normalization, accepting redundancy and data dependencies to improve data performance. Data - Entity (instance, records)

Object Properties

Object properties:

• Encapsulation: Objects hide their attributes, state, and behavior from other objects.
• Inheritance: An object can inherit attributes and behavior from other objects.
• Overriding: The ability to change or modify inherited attributes or behavior.
• Composition: An object can be composed

Digital Awareness

When you want to receive digital information from the outside: The business card input channels are available, usually in groups of 8 bits, to which binary information is assigned by a program. These can be assigned to an internal variable state of a byte by a reading instruction that may have a port. There can be one or more bytes of input, assigning each an address.

Analog Outputs

To send analog control signals to the outside, the tallies have one or more channels of output through their respective A/D converters. A 1V analog converter generates a constant proportional to the numerical value of the digital data that it has on its input lines. Internally, they have a 5V memory. Different voltage ranges can be obtained using... Continue reading "Digital and Analog Signals: Input and Output Channels" »

Essential Linux Commands for File Management

Basic Operations

• mkdir /Destination/Name: Creates an empty directory named Name at the specified Destination.
• touch /Source: Updates the access and modification date of the Source file to the current time. If the file does not exist, it creates an empty file.

Copying Files

• cp /Source/Destination: Copies the Source file to the Destination with the same name.
• cp -r /Source/Destination: Recursively copies files from the Source directory to the Destination directory, preserving the directory structure and file names.

Moving Files

• mv -f /Source/Destination: Moves the Source file to the Destination, overwriting any existing file with the same name.
• mv -u /Source/Destination: Moves the Source file to the Destination

Functions in C

Void functions provide a way to emulate what are called procedures in other languages (e.g., PASCAL). They are used when it is not required to return a value. Here is an example that prints the squares of certain numbers:

void square ()
{
int count;

for (counter = 1; count < 10; counter++)
printf ("%d\n", counter * counter);
}

main ()
{
square ();
}

Input and Output Parameters

To use parameters in/out, the formal parameter must be preceded by the ampersand symbol (&), and the current parameter must be a variable (not an expression). Input/output parameters are used when you want a procedure to change the contents of the current variable. The fact that these parameters are explicitly defined as variables makes the programmer aware of... Continue reading "C Programming Language: Functions, Pointers, and Files" »

Test Strategy

• Test Planning
• Design test cases
• Test Run
• Collection and evaluation

The software is tested to discover errors made inadvertently when carrying out their design and construction.

The tests are a set of activities you can plan ahead and carry out systematically. For this reason, you must define the process of software engineering template for software testing.

A software testing strategy should include: evidence of low-level, high level evidence.

Verification: a set of activities to ensure that software correctly implements a specific function.

Validation: different set of activities to ensure that software built is consistent with customer requirements.

Only once the software architecture comes into play is completed Independent Test Group.

Starting a Session and Destroying Variables (inicio.php)

session_start();
unset($_SESSION["host"]);

Creating a Session and Attempting a Connection (marco.php)

session_start();
$conn = @mysql_connect($host, $user, $password) or die("Incorrect user or password");
@mysql_select_db($db, $conn) or die("Cannot open the DB");

Assigning Connection Parameters to Session Variables

$_SESSION["host"] = $host;
$_SESSION['User'] = $user;

Starting a Session, Connecting to the Database, and Sending an Insertion Query (altas.php)

<?
 session_start();
 $conn = mysql_connect($host, $user, $password) or die("Incorrect user or password");
 mysql_select_db($db, $conn) or die("Not selected");
 $query = "insert into departments values ($dep, '$nom', '$crazy')";
 $result

Features of Free Software

Free software provides the following freedoms:

• The freedom to run the program for any purpose.
• The freedom to study how the program works and adapt it to your needs.
• The freedom to redistribute copies so you can help others.
• The freedom to improve the program and release improvements to the public, so that the whole community benefits.

Sharing Resources in Windows

To share network resources in Windows, you need to ensure that file and printer sharing is enabled in the local area network configuration. To do this, go to "Network Connections", right-click on "Local Area Connection", and select "Properties".

Types of Users

• Administrator or Root: Responsible for configuration and maintenance.
• User: Uses the system and accesses resources