Types of computer systems

Functions of a PC.

The main functions any computer is designed to perform are: input, processing, output and storage.

What is the difference between mainframe and microcomputer? Describe their characteristics and functions. What are two main types of PCs? Describe different kinds of portables (laptops, tablet PCs, PDAs, wearable computers).

Mainframe computers are the largest and most powerful. They usually fill a whole room and are sometimes referred to as mainframes or computer installations. Mainframes are large, powerful, expensive computers that are operated by a team of professionals and are used for large-scale computing purposes in banks, big companies and in large institutions like universities or government departments. The most powerful mainframes are called supercomputers.

The most common type of computer is the microcomputer, sometimes called personal computer.

A PC is a computer designed to meet the needs of a single person. It is used by an individual, usually in an interactive mode. There is a wide variety of PCs but two common types are desktop computers and portables. A desktop PC has its own processing unit (or CPU), monitor and keyboard. It is used as a personal computer in the home or as a workstation for group work.

A laptop (also called a notebook PC) is a lightweight computer that you can transport easily. It can work as fast as a desktop PC, with similar processors, memory capacity, and disk drives, but it is portable and has a smaller screen.

A tablet PC refers to a laptop or slate-shaped mobile computer, equipped with a touchscreen or graphics tablet/screen hybrid to operate the computer with a stylus or digital pen, or a fingertip, instead of a keyboard or mouse. It looks like a book, with an LCD screen which you can fold and rotate 180 degrees.

A personal digital assistant or PDA is a tiny pocket-sized computer which can be held in one hand. The term PDA refers to a wide variety of handheld devices, palmtops, smartphones and pocket PCs. For input, you type at a small keyboard or use a stylus - a special pen used with a touch screen to select items, draw pictures, etc.

A wearable computer runs on batteries and is worn on the user's body, e.g. on a belt, backpack or vest; it is designed for mobile or hands-free operation, often incorporating a microphone and a head-mounted display.

4. Types of keyboards (standard keyboards, multimedia keyboards, gaming keyboards, keyboards of laptops/notebooks, GKOS keyboard, virtual keyboards, on-Screen Keyboard, foldable (flexible) keyboards), groups of keys of a standard keyboard (alphanumeric keys, numeric keypad, function keys, cursor keys, Page Up, and Page Down, dedicated keys, Windows key, application key, etc).

A keyboard is a typewriter-like device that allows the user to type in text and commands to the computer. Keyboard is the earliest and one of the most commonly used input devices. There are different types of computer keyboards. Standard keyboards, such as the 101-key US traditional keyboard 104-key Windows keyboards, include alphabetic characters, punctuation symbols, numbers and a variety of function keys. Keyboards on laptops and notebook computers usually have a shorter travel distance for the keystroke and a reduced set of keys. Keyboards with extra keys, such as multimedia keyboards, have special keys for accessing music, web and other frequently used programs and features, such as a mute button, volume buttons or knob and standby (sleep) button. Gaming keyboards have extra function keys, which can be programmed with keystroke macros. For example, 'ctrl+shift+y' could be a keystroke that is frequently used in a certain game. For example, the GKOS keyboard has been designed for small wireless devices.

Virtual keyboards project an image of a full-size keyboard onto a surface. Sensors in the projection unit identify which key is being "pressed" and relay the signals to a computer or personal digital assistant. There is also a virtual keyboard, the On-Screen Keyboard, for use on Windows.

The On-Screen Keyboard is an image of a standard keyboard which the user controls by using a mouse to hover over the desired letter or symbol, and then clicks to enter the letter.. Touchscreens can be used as a keyboard - the user interacts with the computer by lightly pressing their finger on a touch-sensitive-area of the monitor screen. Foldable (flexible) keyboards are made of soft plastic which can be rolled or folded on itself for travel. A standard PC keyboard has various groups of keys. Alphanumeric keys - these represent letters and numbers, arranged as on a typewriter. A numeric keypad appears to the right of the main keyboard and contains numeric and editing keys;

Function keys appear at the top of the keyboard and can be programmed to do special jobs.

Cursor keys include 'arrow keys' which move the insertion point, and keys such as Home, End, Page Up, and Page Down, which let you move around documents. Dedicated keys are used to issue commands or produce alternative characters. For example: Ctrl changes the functions of other keys (e.g. Ctrl + X cuts the selected text).

Windows key opens the Windows Start menu. This key can also be used in combination with other keys to open utilities. For example, pressing the Windows key in combination with the F key opens the Search utility. Application key is used for quick access to shortcut menus and help assistants in Windows.

5. Input devices: a mouse (a mechanical mouse, an optomechanical mouse, an optical mouse, a cordless (wireless) mouse; main functions); touch panels; light pens; joysticks; microphones.

A mouse is a pointing hand-held device for use with a graphical user interface that lets you move a pointer (or cursor) and select items on the screen thus simplifying user's orientation on the display.

A scroll wheel lets you move through your documents or web pages. The pointer looks like an I-bar, an arrow or a pointing hand. The mechanical mouse is a simple, hard rubber ball mouse which has sensors that detect the movements of the mouse and translate them in moving the pointer on the screen.

The optomechanical mouse works on the same principle. The rollers have wheels on the end of them with evenly spaced holes. As the wheels spin, a light-sensitive optical device counts the number of holes that pass by and converts them to an "X" and "Y" axis.

An optical mouse has an optical laser sensor instead of a rubber ball and rollers underneath. The lasers detect the movement of the mouse and move the pointer accordingly. A cordless (wireless) mouse has no cable; it sends data via infrared signals or radio waves.

Mouse actions:

- to click, press and release the left button.

- to double-click, press and release the left button twice.

- to drag, hold down the button, move the pointer to a new place and then release the button.

- to right-click, press and release the right button; this action displays a list of commands.

In portable computers touch panels or touchpads are used instead of manipulators. Moving a finger along the surface of the touch pad is transformed into the cursor movement across the screen.

A light pen is a photosensitive penlike instrument with a light sensitive tip that is used to draw directly on a computer video screen or to select information on the screen by pressing a clip in the light pen or by pressing the light pen against the surface of the screen. The pen contains light sensors that identify which portion of the screen it is passed over. It can be used for drawing directly on the monitor screen or for reading printed optical characters or barcodes.

A joystick is a pointing device composed of a vertical lever that moves in multiple directions to navigate a cursor or other graphical object on a computer screen precisely and at high speed. It is particularly good for playing fast action games.

Microphone is a device used to input sound. You can also interact with your computer by voice with a voice-recognition system that converts voice into text, so you can dictate text directly onto your word processor

or email program.

6. Scanners (main functions, a flatbed (desktop) scanner, a film scanner, a hand held scanner, a barcode scanner, a pen scanner); digital cameras, camcorders, webcams: main functions and technical characteristics.

Input devices such as scanners and cameras allow you to capture and copy images into a computer.

A scanner is a peripheral that reads images and converts them into electronic codes which can be understood by a computer.

There are different types.

A flatbed (desktop) scanner is built like a photocopier and is for use on a desktop; it can capture text, colour images and even small 3D objects.

A film scanner is used to scan film negatives or 35 mm slides - pictures on photographic film, mounted in a frame. Hand held scanners are small manual devices that are passed manually across the surface of the image to be scanned. Scanning in this manner requires a steady hand, as an uneven scanning rate would produce distorted images.

Barcode scanners read barcodes on the products sold in shops and send the price to the computer in the cash register.

A pen scanner looks like a pen; you can scan text, figures, barcodes and handwritten numbers.

A digital camera doesn't use film. Photos are stored as digital data (bits made up of 1s and 0s), usually on a tiny storage device known as a flash memory card. You can connect the camera or memory card to a PC and then alter the images using a program like Adobe Photoshop, or you can view the images on a TV set. Many printers have a special socket so that you can print images directly from a memory card or camera.

A camcorder (camera+recorder), or digital video camera, records moving pictures and converts them into digital data that can be stored and edited by a computer with special video editing software. Digital video cameras are used by home users to create their own movies, or by professionals in computer art and video conferencing.

Webcams (short for Web cameras) let you send and receive live video pictures through the Internet. They're primarily used for video conferences - video calls - but they can be used to record photos and video onto your hard disk. The resolution of webcams is expressed in megapixels (million pixels). Webcams connect to the PC via a USB (universal serial bus) or FireWire port; they display video at 24 to 30 frames (pictures) per second. Some include a headset with a microphone and earpiece.

7. What is computer data processing? Five basic operations characteristic of all data process­ing systems.

Computer data processing is any computering process that converts data into information or knowledge. Data-processing systems are often referred to as information systems to emphasize their practicality

Five basic operations characteristic of all data processing systems are defined as follows

 Inputting is the process of entering data, which are collected facts, into a data processing system.

 Storing is saving data or information so that they are available for initial or for additional processing.

 Processing represents performing arithmetic or logical operations on data in order to convert them into useful information.

 Outputting is the process of producing useful information, such as a printed report or visual display.

 Controlling is directing the manner and sequence in which all of the above operations are performed.

Computer data processing systems have four main advantages:

 Accuracy. Once data have been entered correctly into the computer component of a data processing system, the need for further manipulation by humans is eliminated, and the possibility of error is reduced. Computers, when properly programmed, are also unlikely to make computational errors.

 Ease of communications. Data, once entered, can be transmitted wherever needed by communications networks. These may be either earth or satellite-based systems.

 Capacity of storage. Computers are able to store vast amounts of information, to organize it, and to retrieve it in ways that are far beyond the capabilities of humans. The amount of data that can be stored on devices such as magnetic discs is constantly increasing. All the while, the cost per character of data stored is decreasing.

 Speed. The speed, at which computer data processing systems can respond, adds to their value.

The response required might be a fraction of a second.

8. What is CPU? Three main parts of the unit (a control unit, ALU, registers), their components, main functions, sequence of main operations.

The nerve centre, the brain and the heart of a PC is the central processing unit or CPU. This unit is built into a single microprocessor chip - an integrated circuit - which executes program instructions and supervises the computer's overall operation

The unit consists of three main parts:

1. The control unit, which examines the instructions in the user's program, interprets each instruction and causes the circuits and the rest of the components -disk drives, monitor, etc. - to be activated to execute the functions specified, selects instructions and data from memory, and controls the flow between main storage and the arithmetic-logical unit.

The control unit has the following components:

 a counter that selects the instructions, one at a time, from memory;

 a register that temporarily holds the instructions read from memory while it is being executed;

 a decoder that takes the coded instruction and breaks it down into individual commands

necessary to carry it out;

 a clock, which produces marks at regular intervals.

The sequence of control unit operations is as follows:

• The next instruction to be executed is read out from primary storage into the storage register.

• The instruction is passed from the storage register to the instruction register.

• The operation part of the instruction is decoded so that the proper arithmetic or logical operation can be performed.

• The address of the operand is sent from the instruction register to the address register.

• At last the instruction counter register provides the address register with the address of the next instruction to be executed.

2. The arithmetic logic unit (ALU), which performs mathematical calculations (addition, subtraction, multiplication, division and exponentiation, etc.) and logical operations (and, or, etc.). Data enter the ALU and return to main storage through the storage register.

3. The registers, which are high-speed units of memory used to store and control information. One of these registers is the program counter (PC) which keeps track of the next instruction to be performed in the main memory. Another is the instruction register (IR) which holds the instruction that is currently being executed.

9. Bits - basic units of memory: binary notation, binary digit, byte, kilobyte, megabyte, gigabyte). What is a standard system for the binary representation of characters?

Information is processed and stored in computers as electrical signals.

To represent these two conditions we use binary notation in which 1 means ON and 0

means OFF. This is the only way a computer can 'understand' anything. Everything about

computers is based upon this binary process. Each 1 or 0 is called a binary digit or bit. 1s and 0s are grouped into eight-digit codes that typically represent characters (letters, numbers and symbols). Eight bits together are called a byte.

The majority of computers use a standard system for the binary representation of characters.

This is the American Standard Code for Information Interchange, known popularly as ASCII (pronounced 'ask-key'). There are 256 different ways of combining 0 and 1 bits in a byte. So they can give us 256 different signals. However, the ASCII code only uses 128 bytes to represent characters. The rest of the bytes are used for other purposes.

The first 32 codes are reserved for characters such as the Return key, Tab, Escape, etc. Each letter of the alphabet, and many symbols (such as punctuation marks), as well as the ten numbers, have ASCII representations. What makes this system powerful is that these codes are standard. In order to avoid astronomical figures and sums in the calculation of bytes, we use units such as kilobytes, megabytes and gigabytes. One kilobyte is 1,024 bytes (2№є) and it is represented as KB, or more informally as K. One megabyte is equivalent to 1,024 KB, and one gigabyte is 1,024 MB.

We use these units (KB, MB, GB) to describe the RAM memory, the storage capacity of disks and

the size of any application or document.

10. How does a monitor work? Types of monitors (CRT, TFT-LCD, Plasma displays). Main functions of video projectors, multimedia speakers. What is the difference between earphones, earbuds, stereophones, headsets and cans?

It is a piece of electrical equipment which displays images generated from the video output of computers, without producing a permanent record. The monitor comprises the display device, simple circuitry to generate and format a picture from video sent by the signals source, and usually an enclosure. The monitor is controlled by a separate circuit board, known as the display adaptor. The video card processes images and sends signals to the monitor.

Older monitors are based around a cathode ray tube (CRT), similar to a traditional TV set. At the back of the tube there is a negatively charged cathode and three electron guns - each gun shoots out a beam of electrons for each of the primary colours: red, green and blue. These electrons strike the inside of the charged screen which is coated with substances called phosphors (there are different materials for each of the three colours) that glow when struck by electrons and create colours.

CRTs are cheap, but they are heavy, can flicker and emit radiation.

Most newer monitors typically consist of a TFT-LCD. A Liquid Crystal Display (LCD) is made from flat plates with a liquid crystal solution between them. The crystals block the light in different quantities to create the image. Active-matrix LCDs use TFT (thin film transistor) technology, in which each pixel has its own transistor switch. TFT systems offer a wider angle of vision and high-quality images, they are flat and take up less space, use less power than CRTs,

Plasma displays have many advantages: high-contrast images and bright colours, generated by a plasma discharge which contains noble, non-harmful gases. Gas-plasma TVs allow for larger screens and wide viewing angles, perfect for movies.

Video projectors are used when audiovisual presentations are on a laptop connected to a front-

screen projector which displays the images on a distant screen or white wall.

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