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

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

Classification of Computer Memory by Function

Core Memory Components

• Central Memory: The portion of the CPU where instructions and data necessary for a given process are stored.
• Cache Memory: Stores frequently used instructions and data, significantly improving computer performance.
• Conventional Extended Memory: Accessed via specific software that forces the microprocessor into protected mode, or by utilizing 386/486 capabilities to allocate expanded memory as conventional memory.
• Conventional Expanded Memory: Memory inaccessible to standard MS-DOS programs. It requires an Expanded Memory Manager (EMM) to allocate pages of bytes as needed. Only EMS-compatible software can utilize this.

Primary Memory Types

• RAM (Random Access Memory): Classified by

Understanding Structural and Behavioral Models

A structural model is used to analyze the structure of a system of objects and their relationships. This model is developed in layers. Within this framework, structural modules (mod_estrutural) are used to mount interaction diagrams that show the relationship between modules and subsystems.

The Role of Interaction Diagrams

An interaction diagram (D_interação) is a behavioral specification that includes a sequence of message exchanges between a set of objects to achieve a purpose. These should be used when you wish to view the behavior of various objects within a single use case, based on the messages passed between them. The strength of these diagrams is their simplicity.

Sequence and Collaboration

AGP Bus: High-Speed Graphics Interface

The AGP bus was developed to release the occupation of system buses as much as possible when working with the graphics card. Since graphics cards require a significant amount of data, especially when working in 3D, they previously kept buses busy and prevented other peripherals from connecting. The general characteristics for this bus include:

• Speeds are much higher than the peak of the system bus.
• It incorporates DMA (Direct Memory Access).
• It can access main memory for instructions and programs while performing read/write operations.
• It can use main memory as video memory.
• There are no waiting times because it does not have to compete for system buses.

HyperTransport Technology

HyperTransport is a universal... Continue reading "High-Speed Data Transfer: AGP, HyperTransport, and Parallel Ports" »

Wide Area Networks (WAN)

A Wide Area Network (WAN) spans a large geographic area, such as a country or continent. Its primary function is to connect networking and terminal equipment located at great distances. These networks rely on an infrastructure of powerful switching nodes to facilitate the continuous flow of significant amounts of information. WANs are considered public networks because they handle traffic from diverse locations, enabling users worldwide to transmit data across vast distances.

Network Protocols

A network protocol is a set of rules specifying the exchange of data or commands for communication between systems. These rules allow information to flow between computers that might otherwise handle different languages. If two computers... Continue reading "Understanding Wide Area Networks and Communication Protocols" »

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" »

Software: Definition and Functions

Software is the intangible component of any computer system. It consists of a collection of rules and guidelines that establish the relationship between the user and the machine.

Functions of Software

1. To reduce manual entry of information.
2. Provide communication media between man and machine.
3. Encourage greater use of media and reduce the processing time of files.
4. Provide routines that automatically perform repetitive, classified work.

Software Classification

System Software

A series of programs that facilitate man-machine communication, permitting its proper exploitation.

Application Software

Programs developed to solve specific problems. These can be classified into:

Basic or Utility Programs

These are applications whose... Continue reading "Software Fundamentals: Classification and Acquisition Methods" »

Data Link Layer Tasks and Error Handling

The Data Link Layer is responsible for media access control in shared environments and comprehensive error handling.

Communication Design and Error Management

• Data Division: Information is divided into blocks carrying a sequence number and an error detection code. If an error occurs, the block is re-received.
• Information Control: All necessary information is included to ensure the receiver can reconstruct the data.
• Error Correction: Detecting and correcting errors within the communication channel.
• Flow Control: Managing the rate of data transmission.
• Control Dialog: Managing transmission shifts and communication flow.

Design of the Link Layer

The design focuses on providing connection-oriented and reliable services... Continue reading "Data Link Layer Functions and Error Control" »

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