Types of computer systems

Computers can be divided into different types, depending on their size and power. There is an increasing variety of computers of different sizes and designed for different purposes.

Mainframe computers are the largest and most powerful. They can handle large amounts of information very quickly supporting multiple users at the same time and can support more simultaneous processes than a PC. A terminal, consisting of a keyboard and a monitor, is used to input and output information on a mainframe. The central system is a large server connected to hundreds of terminals over a network. 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.

It gets the name from the tiny electronic device, called the microprocessor that does the actual processing. 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. PCs are found in many businesses and are popular for home use. They are becoming as common as the television and the telephone in the household.

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. Desktops are small enough to sit on an office desk and are relatively cheap. Typical examples are the IBM PC and the Apple Macintosh. It's designed to be placed on your desk. Some models have a vertical case called a tower.
	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. Laptops are capable of the same tasks as a desktop computer, although they are typically less powerful for the same price. They contain components that are similar to their desktop counterparts and perform the same functions, but are

miniaturized and optimized for mobile use and efficient power consumption. Modern notebooks have a TFT (Thin Film Transistor) screen that produces very sharp images.

In addition to a built-in keyboard, they may utilize a touchpad (also known as a trackpad) - a sensitive pad that you can touch to move the pointer on the screen - or a pointing stick for input, though an external keyboard or mouse can usually be attached.

They offer a lot of connectivity options: USB (Universal Serial Bus) ports for connecting peripherals, slots for memory cards, etc.

They come with battery packs, which let you use the computer when there are no electrical outlets available.

One of the reasons that notebook portables are popular is because their screens and keyboards are just big enough to use comfortably for word processing and they are even used for multimedia.

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. Your handwriting can be recognized and converted into editable text. You can also type at the detached keyboard or use voice recognition. It's mobile and

versatile. The form factor offers a more mobile way to interact with a computer. Tablet PCs are often used where normal notebooks are impractical or do not provide the needed functionality.

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, smartphonesand 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. Some

models incorporate handwriting recognition, which enables a PDA to recognize characters written by hand. Some PDAs recognize spoken words by using voice recognition software. Some include a virtual keyboard which pops up when you want to enter email text or a WAP address. They are also equipped with software to handle e-mail and surf the Web via wireless technology, without cables. You can hear popular MP3 music or record your ideas through its built-in voice recorder. Once at home you can synchronise data with your desktop PC. PDAs support mobile computing, but almost never run any desktop software. They can be used as cellphones or as personal organizers for storing notes, reminders and addresses.

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. Some devices are equipped with a wireless modem, a keypad and a small screen; others are voice-activated, worn like a scarf and can access

email or voice mail. Wearable computers are especially useful for applications that require computational support while the user's hands, voice, eyes or attention are actively engaged with the physical environment. Users of wearable technology consider themselves 'cyborgs'. This term comes from 'cybernetic organism', referring to a being that is part robot, part human.