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

A computer virus is a type of computer program that, when executed, replicates itself by modifying other computer programs and inserting its own code.^[1] When this replication succeeds, the affected areas are then said to be 'infected' with a computer virus.^[2][3]

Virus writers use social engineering deceptions and exploit detailed knowledge of security vulnerabilities to initially infect systems and to spread the virus. The vast majority of viruses target systems running Microsoft Windows,^[4][5][6] employing a variety of mechanisms to infect new hosts,^[7] and often using complex anti-detection/stealth strategies to evade antivirus software.^{[8][9][10][11]} Motives for creating viruses can include seeking profit (e.g., with ransomware), desire... Continue reading "Understanding Computer Viruses and Network Topologies" »

Javascript Continued

Proximity

Proximity is all about using visual spaces to show relationships in your content. We can group the items in blocks of text or elements in the graphic to take visual emphasis.

White Space

White space, also known as negative space, refers to the spaces between your content, between lines, and even the margins. White space defines and separates different sections.

Alignment

We can separate text boxes, images, etc. by imagining their content as a range inside of a grid. Centering the images to the text and using equal size margins can create a visually pleasing alignment.

Contrast

Contrast means that one item is different from another. We can create contrast using color, size, shape, or contrasting styles of text. Hierarchy, a visual technique... Continue reading "Using Proximity, White Space, Alignment, Contrast, and Repetition in Design" »

Introduction to Architecture

• Instruction Set Architecture (ISA): An assembly language programmer's view of the microprocessor.
• Assembler: Translates symbolic assembly language code into binary machine language code.

Computer Performance Metrics

• Execution Time (Response Time): Time to complete a program or task.
• Throughput (Bandwidth): Number of programs or tasks completed per time unit.
• Execution Time (t_exec, i.e., elapsed time, wall time, real time, response time): Elapsed seconds from start to finish. Includes:
  • Executing instructions
  • Disk access
  • Memory access
  • I/O activities
  • OS overhead
• User CPU Time (t_cpu(user)): Seconds the CPU spends executing the program's instructions.
• System CPU Time (t_cpu(sys)): Seconds the CPU spends executing OS (kernel) instructions

Weight of 30 Students - Minimum, Maximum, Average and Standard Deviation - Histogram

a = [71 82 65 75 77 91 59 84 89 81 73 91 82 75 96 85 69 76 81 92 84 79 77 95 81 79 84 85 76 82]

a = Columns 1 through 12

71 82 65 75 77 91 59 84 89 81 73 91

Columns 13 through 24

82 75 96 85 69 76 81 92 84 79 77 95

Columns 25 through 30

81 79 84 85 76 82

Maximum: 96

Minimum: 59

Average: 80.5333

Standard Deviation: 8.4516

Histogram

Plot the value of the cosine within [0 2π] with a step of π/20.

Label the axes and add a title.

Add to that graph the sine function. Use hold command.

Place legends to distinguish both graphic

x = 0:pi/20:2*pi

0 0.1571 0.3142 0.4712 0.6283 0.7854 0.9425 1.0996 1.2566

1.4137 1.5708 1.7279 1.8850 2.0420 2.1991 2.3562 2.5133 2.6704

2.8274 2.9845 3.1416... Continue reading "Statistics and Trigonometry: Student Weights and Cosine Function" »

Design of Webpages

There are 2 distinct phases:

• Layout: it organizes written and multimedia spaces and contents.
• Interface: is the set of commands and methods that facilitate the interaction between the user and the system

We cannot move ahead with the creation of a web page without knowing what we want to show, the topic and the quantity of information that we will put in it. We shall also decide the title of the web page, its header and its logo, since they will give a sensation of continuity and greater professionalism.

CMS

The Content Management Systems (CMS) are applications installed on the server that enable us the creation of dynamic web pages and allow us to design the site independently of the content. When we administer a CMS, we define... Continue reading "Webpage Design and Security Threats" »

Chapter 1 Introduction to Services

3.1. Service Terminology Service

a service is a software program that makes its functionality available via a technical interface, called a service contract.

Figure 3.1. The symbol used to represent an abstract service.

Service Contract

The symbol used to represent a service contract is displayed in Figure 3.2.

Service Capability

A service contract can be broken down into a set of service capabilities, each of which expresses a function offered by the service to other software programs.

Figure 3.4. A Purchase Order service contract with four service capabilities.

Service Consumer

A service consumer is software program when it accesses and invokes a service—or, when it sends a message to a service capability

Service

1. Visibility of System Status

The system should always keep users informed about what is going on, through appropriate feedback within a reasonable time.

2. Match Between System and the Real World

The system should speak the user's language, with words, phrases, and concepts familiar to the user, rather than system-oriented terms. Follow real-world conventions, making information appear in a natural and logical order.

3. User Control and Freedom

Users often choose system functions by mistake and will need a clearly marked "emergency exit" to leave the unwanted state without having to go through an extended dialogue. Support undo and redo.

4. Consistency and Standards

Users should not have to wonder whether different words, situations, or actions... Continue reading "10 Usability Heuristics for User Interface Design" »