Text 5. Computer viruses

Today mass application of PCs, unfortunately, is connected with occurrence of a sort of programs which interfier normal work of the computer discs, destroy file structure and damage the stored information. Along with an easy approach to all resourses of the machine we can face the danger, which recently has received the name of a “computer virus”.

A computer virus is a parasitic program written intentionally to alter the way computer operates without user’s permission or knowledge. This program can copy itself and install its replicas into software, placed in files, discs, documents, etc.

According to the mode of action and objects, being infected, there are:

1. file viruses, with the expance exe., com. and overlane ones;

2. load viruses, which penetrate into initial disc sector, where the operating system loader is set; they start working while computer loading and always infect set-in diskette;

3. viruses infecting Word and Windows documents, as a rule they affect Normal. dot.

MACRO VIRUSES, or macros, are malicious programs that are designed to replicate themselves from file to file and can destroy or change data. Macros are written in files by such programs as Microsoft Word and Microsoft Excel. They can be transferred across platforms and spread whenever you open an infected file.

TROJAN HORSES are programs that appear to serve some useful purposes or provide entertainment, which encourages you to run them. But the program also serves a convert purpose – to damage files or place a virus on your computer. Trojan horses are not viruses because they don’t replicate and spread like a virus. Because they are not viruses, files containing them can’t be repaired.

WORMS are programs that replicate without infecting other programs. Some worms spread by copying themselves from disc to disc. They search for specific types of files on a hard disc or server volume, and try to destroy or damage them. Other worms replicate only in memory, creating myriad of copies, all running simultaneously, which slows down the computer. Like Trojan horses, they are not viruses and can’t be repaired.

Both Trojan horses and worms must be deleted from your computer.

Черкаський політехнічний технікум

Текст № 5

для студентів III курсу, 6 семестр (ПС)

Викладач Горпинко В.П.

Text № 6 program structure

FLOWCHARTS

Before writing programs one should write flowcharts. This helps to ensure that all steps are got into a program and in the right order. A flowchart is a kind of a plan of a program’s logical flow. Once a flowchart is written, you can translate it into a program by writing one or more statements for each step in the flowchart.

However, when you begin to plan more complex programs, you’ll find that the flowcharts also become more complex. When you have a great many steps and a great many branches, you simply can’t find a place for all of them on the flowchart. This makes it very hard to check the flowchart you’ve written to be sure that you haven’t left anything out. To handle more complex programs, you need another way of planning them.

MODULAR DESIGN

In engineering, programming and other fields a module is a self-contained unit that performs one specific task, which is needed to accomplish a large task. For example, the word module is used in the space program to refer to a part of a spaceship that performs a specific task. A lunar landing module lands the Moon. A power module provides the ship in space. A waste-disposal module gets rid of garbage. All of theses modules are necessary for getting spaceships to the Moon and back.

In computer program, a module is a self-contained part of the program that performs a specific programming task. For example, a program might have an input module and a print module. A program that is divided into modules in planning and programming stages has a modular design.

A modular program has a top-down structure because you plan it, you start at the “top” with the most general module and walk your way “down” to include all the modules that make up that module. This allows you to break a complex program into parts to make programming more efficient and easier.

Черкаський політехнічний технікум

Текст № 6

для студентів III курсу, 6 семестр (ПС)

Викладач Горпинко В.П.