Glossary - C

Cathode ray tube (CRT)

A cathode ray tube is a type of electron accelerator that is enclosed in a vacuum tube and includes a fluorescent material that glows when it is struck by a stream of electrons. The cathode ray tube was invented in 1897 by the German physicist Karl Ferdinand Braun. Cathode ray tubes are used primarily in display devices such as televisions, computer monitors and oscilloscopes. TV screens employ an electromagnetic deflection of the electron beam while oscilloscopes employ an electrostatic deflection of the electron beam. Black and white screens use a single beam while color screens use three colored beams with a shield mask. The main weakness of classic CRT screens is that the depth of the display device must be rather large to accommodate the tube. The advantages include great color and the ability to view the screen from a variety of angles.

Central processing unit (CPU)

The central processing unit or CPU, also called the "processor", is the "brain of the computer". It carries out each instruction of the program in sequence to perform the basic arithmetical, logical, and input/output operations of the system. Two typical components of a CPU are: The arithmetic logic unit (ALU), which performs arithmetic and logical operations and the control unit (CU), which extracts instructions from memory and decodes and executes them, calling on the ALU when necessary. The performance or speed of a processor generally depends on the clock rate (multiples of hertz) and the instructions per clock, which together are the factors for the instructions per second  that the CPU can perform. Processing performance of computers is increased by using multi-core processors, which essentially means plugging two or more individual processors into one integrated circuit. Ideally, a dual core processor would be nearly twice as powerful as a single core processor. In practice, however, the performance gain is far less, only about fifty percent, due to imperfect software algorithms and implementation. Modern microprocessors appear in everything from automobiles to cell phones and children's toys.

Commercial network

A commercial network management tool is mostly used in (large) corporations. It can log the network traffic passively (sniffing) or examine the logs of proxies, etc. Nothing is installed on the individual computers, the software runs on a central server. They can only log items that pass through the network, but not local items such as the entered passwords, keystrokes or screenshots.

Compact disc (CD)

A compact disc is an optical disc designed to store a digital data. Data is stored in the tracks of a single long spiral that starts in the middle of the media and gradually expands to its edge. Each track can include a digital audio recording (the audio CD) or (computer readable) data (CD-ROM). Cross-track distance is 1.6 microns. A laser light with a wavelength of 785 nm is used to read compact discs. The record (data spiral) is accessible only from the underside of the disk, so a CD recording is one-sided. The entire length of the spiral is ​​about 6 km and the density of the data stored within it is constant. A normal CD has a diameter of 12 cm, but there is also a smaller version with a diameter of 8 cm (as well as a truncated version of the format in the shape of a business card or any other shape). While a CD is 1.2 mm thick, the discs are written from a radius of only 23 mm to 58 mm.

The compact disc was developed in 1979 by Sony® and Philips® as a way of storing and reproducing music. Originally, the goal was to fit a 60-minute audio recording onto a single CD (the length of a long-analog "album"), but Sony® insisted on 74 minutes in order to fit all of “Beethoven's Ninth Symphony” on one CD. Today, most CDs hold eighty-minutes of recorded audio, but variations do occur with some CDs holding up to ninety-nine minutes. Discs longer than 80 minutes may not be readable in all players.

The CD format is rapidly being eclipsed by the disc DVD, whose price has come down significantly over the years, along with DVD media player prices. The DVD is a direct successor to the CD as evidenced not only by its outer appearance, but also by the digital data recording technology. Each layer on a DVD can hold more than six times the amount of data on a CD. CD media lifetime is about 8 years.


A computer is a programmable machine which can execute a prerecorded list of instructions (a program) and respond to new instructions that it is given (typically inserted by input devices or data). Technically there are two basic types of computers, analog and digital, but we can divide computers to many categories by various features, for example desktop and laptop computers. In general, computers require the following hardware components: central processing unit (CPU) which is the heart of the computer that performs most calculations or executes instructions. The main memory enables the computer to store, at least temporarily, data and programs. A mass storage device or auxiliary data storage provided by an internal hard disk and may be supplemented by other media such as external hard disks, USB flash drives, or optical drives that use CD-ROMs or DVD-ROMs. Many computers today also include a specialized graphic processor, with dedicated memory, for handling the display of complex graphics, such as for three-dimensional simulations and games. Peripheral equipment including input devices (i.e., keyboard, mouse) and output devices (i.e., monitor, printer), as well as the circuitry and cabling that connect all the components.

Computer File

Computer files are the modern counterpart of paper documents which traditionally were stored in office or library files and thus the source of the term “file”. In computer language,  the file is a named sequence of bytes stored on any data medium (e.g., hard disk, floppy disk, CD, flash drive). Each file has its name, length and possibly other attributes used by the operating system. The content of the file may contain a different data (text, binary data containing the machine code of any application, file, etc.). The physical arrangement of files on a data medium is dependent on the user’s filing system so that they can be easily accessed. Each operating system (which uses a file system) provides the user a suitable form of administration, such as deleting files, copying, or renaming can be done through both commands and programs in a graphical user interface.

Computer game

A computer game is a game that runs and is played on a computer, typically for entertainment purposes. Video games are run on the game console. Games are software that can be published on any media (DVD, CD, floppy) or distributed via the Internet.

Computer games feature a virtual world or environment that players can interact with via the computer’s components (mouse, keyboard, joystick, joypad, etc.). Many games challenge the player to accomplish a goal or goals. The goal may be to complete a quest within a certain period of time, to defeat a virtual opponent in fight simulation, to win a race or to meet other objectives depending on the theme, genre and the intentions of the game’s developers. Game themes can be absolutely anything, (e.g., movies, historical and fictional war scenarios, ordinary life, detective investigations, board games, etc.).

Some of the most popular genres include:

  • Strategy
  • Adventure
  • 3D action
  • Simulators
  • Arcade

Modern computer games often have specific hardware requirements that tend to increase in sophistication as new technology is developed. Typical requirements include control devices, sound card, graphics accelerator and other hardware components that are not essential to the computer’s basic operations.

Developing a sophisticated computer game can take several years. Games often employ cutting-edge technology that demonstrates the possibilities that have become available as hardware and software development progresses.

While playing, it is recommended that gamers follow the principles of ergonomics and correct posture, and take short breaks every so often so the body does not become fatigued—just as users at a computer workstation are advised to do.

With the expansion and accessibility of the Internet, interest in online games has increased. Some of the most popular games include “Massively multiplayer online role-playing games” (MMORPG) that enable players to live the life of a virtual character in a virtual world and interact with other players who are also part of the virtual world.  But beware! MMORPGs can be addictive and time-consuming, and excessive gaming can have a negative impact on social relationships and physical health.

Computer icon

A computer icon is a graphic symbol representing a  feature, function or entity, and can help users navigate a computer system or mobile device. In computer applications, icons are used to quickly execute commands or open programs and documents. The function that is assigned to the icon is accessible by a single or double click on the image.

Typically, operating systems allow users to edit the appearance of objects by assigning their own icons. The icon is composed of a number of images so it can be used in a wide range of situations, such as a modern LCD as well as a ten-year-old monochrome monitor. Each of the images inside icons is designed for viewing under certain circumstances. They have different sizes (or resolutions) and color depth.

Microsoft Windows® defines a standard size (16x16, 32x32, 48x48) and standard color depth (16 colors, 256 colors, 16.8 colors) that should be present in each icon for general use.

A computer icon’s  placement on the screen  in relation to other icons may provide further information to the user about their function. Commonly, icons can do each of these functions and assist with the user’s experience far more effectively than words on the screen.

Computer keyboard

The computer keyboard was derived from the typewriter keyboard or telex. Keyboards are used to control computers and to insert characters into documents.  Standard computer keyboards are powered by the computer and communicate with a serial line. A computer keyboard contains buttons that are called keys. Generally, a keystroke causes the sending of a character as an input. By default, some keys serve only to execute predefined functions. Sending some symbols requires the stroke and holding several keys simultaneously or sequentially. The keyboard is also important as an input device for entering passwords, writing reports, etc. There are many different keyboard layouts. These were made to accommodate different needs and provide easy access to different symbols. Usually, this arises from the need to write in a language other than English, but there are also specialized layouts for mathematics, accounting, and programming use. The distribution of characters on computer keyboards copies the standards from typewriters. Some countries use the QWERTY layout, elsewhere QWERTZ, and some use layouts that are very different, for example, the French AZERTY. Key layouts are regulated by the international standard ISO/IEC® 9995 "Information technology - Keyboard layout for text and office systems" from 1997. In earlier years, the keyboard was connected to the computer using a DIN-5 connector, which was later replaced by a slightly smaller Mini-DIN connector, often called the PS / 2, but the method of communication with the computer remained the same. Today, the modern way of connection is the USB.

Keys can be divided into the following groups:

  • Basic alphanumeric keys
  • Numeric keypad
  • Function Keys
  • Special keys
  • Keys for a specific operating system (e.g., Microsoft Windows®)

Companies that produce keyboards include KME©, Apple®, Logitech®, Microsoft® and others.

Computer Monitor

A computer monitor  is the electronic visual display output for computers. The monitor includes the display screen , circuitry, and an box enclosure. Today’s display screen is typically a thin film transistor liquid crystal display (TFT-LCD) thin panel, while older monitors used a cathode ray tube about as deep as the screen size. Since the 1980’s onwards, computers and televisions have been used for both data processing and entertainment, therefore the common aspect ratio of monitors has also changed from 4:3 to 16:9.

Computer mouse

The computer mouse is a small pointing device that converts information from its movements on the surface area (e.g., a desk) to the computer, which is usually presented on the screen as movement of the cursor. In general, a mouse has one or more buttons and may include one or more wheels to facilitate movement. On the bottom of the mouse is the mechanism that senses the mouse’s movements (sensor). The mouse was invented by Douglas Engelbart at the Stanford Research Institute in 1963. It was then introduced to the public on December 9, 1968 by its inventor. Douglas Engelbart had it patented (patent US3541541) on November 17, 1970 as “XY Position Indicator for a Display System." The first company to use the mouse in a commercial environment was the California company known as Apple®, in 1982. After the mouse based on Engelbart's invention which included a moving ball with mechanical sensors, optical mice with LED technology became the norm, circa 1980. The optical mouse was invented by Steve Kirsch. However, it required a special metallic surface with a printed grid, without which it did not work. The first mice were angular and uncomfortable to manipulate. Newer models are ergonomically designed for a comfortable grip, but this is not sufficient prevention against maladies that can occur from excessive mouse use (Repetitive Strain Injury (RSI)). Initially, the mouse connected to a computer via a serial port (RS-232) and for Apple® computers via a fox ADP. Around the year 2000, the PS/2 connector came about, then the USB. Some mice are referred to as a combo, which means that they can use a simple adapter to plug into the USB and PS/2. A wireless mouse uses infrared (IrDA) or radio waves (including Bluetooth®), while the actual transmitter / receiver can be connected to a computer via a serial interface, PS/2 or USB. Despite articles about the possibility of damage to the human eye from optical mice, there is no factual basis for these concerns since optical mice use a Class I - laser device that does not have sufficient power to cause eye damage.

Computer Network

The first computer network was made by George Stibitz in September 1940, as he sent information by teletype machine from Dartmouth College to New York and received results by the same means. From this we can say that computer networking is the connection of two computers linked together for the purpose of sharing information. But today’s networking is more complicated, it is a logical connection of many  computers to facilitate communication.  The communication enables sharing data and information using communication rules called “protocols” which defines the format of the network. Well-known communications protocols are Ethernet used in LANs, the Internet Protocol used primarily in the Internet.  Communication protocol is not the only thing which classifies the network, there are networks with different topology, scale, organizational scope or medium used for transferring data. 

Computer program

In computer science, a program is a sequence of operations that describe the implementation or executing of tasks. Computer programmers can create programs by writing algorithms in a programming language. Previously, this was often implemented directly via the hardware (connecting wires, punch card, etc.). Current programs are usually written in a programming language in source code form, to make the code comprehensible to humans. Written programs can be executed by a computer via an interpreter that may first translate it into machine code, and then execute it directly via a microprocessor. Running a program (i.e., a program residing in the computer’s memory which is then executed by processor) is called a process. The program can run multiple times to create multiple processes. The process resides in the memory and consists of the program and dynamically changing data. This process can be composed of multiple strings. Current multitasking systems run multiple processes, which are performed simultaneously.

Computer user

The computer user generally refers to a person who uses a computer system (including use of its software and hardware). For security purposes, a record of actions carried out or resource management may be required to identify the authorized user. To assist in the identification the individual must create a user account, user name or nickname and password in most cases. Individuals access the system using the computer user interface.

Computer virus

A computer virus is computer software that has the ability to replicate itself and infect a computer without the informed consent or knowledge of the computer user. Certain malware, adware and spyware have been incorrectly termed as a “virus” because they lack the ability to copy themselves. A real virus spreads from one system to another through an executable code when its host is transferred to a target computer; such as being sent over a network or the Internet, email or transported via removable media such as a CD, DVD or USB drive. Infected files residing in a network file system or any instance where a computer can be accessed by another one increases the chances of spreading a virus infection.

The term "computer virus" is considered to be malware, a much broader term which also encompasses several types of malicious software including worms, trojans, and others. Although technically different, viruses are often confused with computer worms and trojans. Unlike a virus, a worm can take advantage of security holes in order to spread itself among other systems, while a trojan appears to be harmless but has an underlying plan. A worm, trojan or virus, once executed, can endanger a computer’s data, operation, or network ability. User awareness of some computer viruses and other malware may be readily apparent while many other types go unnoticed.

The increasing number of computers being connected to local area networks and the Internet is creating an environment for computer viruses to spread. Increased use of email and instant messaging are additional ways computer viruses spread.

Computer worm

A computer worm is a self-replicating computer program that sends copies of itself within a computer network and it can do so without any involvement by the user. A worm doesn’t need to attach itself to an existing program in order to spread. Worms typically cause some harm to the network, most notably by consuming bandwidth.


Crimeware is a distinct type of malware designed to automate financial crime by performing identity theft to access online accounts of users at financial institutions and online retailers for the express purpose of stealing funds from those accounts or performing unauthorized transactions to the benefit of the thief controlling the crimeware. Crimeware is often used to export private information from a network for financial exploitation. Crimeware is viewed as a growing concern in network security as this type of threat seeks to steal confidential information.


A cursor is a pointer that displays on a computer monitor to indicate the location where a user action, such as a mouse click or keystroke, will generate a response from the computer.

When composing text, the cursor can function to insert new text or overwrite existing text. In the insertion mode, new characters are inserted at the exact position of the cursor, while in the overwriting mode, existing characters are replaced at the cursor position. In text editors with a graphical user interface (GUI), the cursor is typically represented by a static or blinking vertical line located between characters.

A mouse cursor or mouse pointer is graphical object that indicates the position where interaction between the computer and the user will occur. It is usually represented by a white arrow (or a solid rectangle in older systems and text interfaces), with the point of activation typically located at the tip of the arrow. This cursor typically invokes different actions depending on its location, and can change its appearance to indicate different functionality.

Examples include:

  • Double arrow – at the edge of a window, for resizing.
  • Hours/ball/circle – when the system is busy
  • Hand – above a hyperlink or while moving an image or document file.
  • Tools – in graphical applications, for example a brush or eraser.

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