Computer are available in different shapes, size and weights, due to these different shapes and sizes they perform different sort of jobs, all the computers are designed by the qualified architectures as per requirement.
Basically there are two types or classes of computers
Analog and Digital Computers
Analog Computer Digital Computer
An analog computer is a type of computer or machine that work on the continuously-changeable aspects of physical phenomena of electrical, mechanical, or hydraulic quantities as input behavior and solve the problem.
In other words analog computers do their jobs on variable input quantities.
In contrast, digital computers work on numerical values called digits .
Analog computers uses continuous variables for mathematical operations and utilizes mechanical or electrical signals, they were commonly used in science and industry for measuring values and other required operations like temperature & volume.
Use of Analog computers is almost obsolete now.
Digital computer that performs calculations and logical operations with 0 and 1 digits, known as binary number system.
Computer of this type represents information by numerical (binary) digits and uses digits for calculations or operations.
digital computer measures discrete values of 0 and 1 and carry out mathematical calculation on them.
Use of digital computers is in every field of science, industry, research labs as well as other human life.
Hybrid Computers are a combination of both digital and analog properties.
In this type of computers, the digital component normally serves as the controller and provides logical operations, while the analog component normally serves as a solver of differential equations.
Hybrid computers measures discrete values (digital) and values that change continuously in magnitude (analog).
In many applications it accepts analog signals, converts them to digital and processes them in digital form and digital data and known as analog-digital computer.
Personal Computer (PC)
PC can be defined as a small, relatively inexpensive computer designed for an
Personal computers first appeared in the late 1970s. One of the first and most popular personal computers was the Apple-II and IBM PC.
The PC is microprocessor based single-user system and used in general computing, surfing the web, playing games or music, editing and other tasks at school, home or business.
Today, the world of personal computers is basically divided between Apple Macintoshes and PCs. It can be categorized in two major types: desktop and laptop .
PC’s Tower model type computers has the power supply, motherboard, and mass storage devices are stacked top of each other in a cabinet.
A computer designed to fit comfortably on top of a desk, typically with the monitor sitting on top of the computer.
Desktop model computers have generally limited editions comparing to Tower model.
A small, portable, too smaller that can sit on your lap. Laptop computers are small in size, low weight and easy to carry anywhere.
It has same approach like a Personal Computer with all applications but portable in nature, it is the best replacement of PC when mobile computing.
It is designed for mobility, miniaturized technology and made for low power consumption but significantly more expensive than desktop systems.
The screen size ranges from 14" to 20", weight is usually around 3 kg.
Notebook is sort of laptop but extremely light-weight personal computer. Notebook computers typically weigh less than 6 pounds (2.2-2.5 kg) and are small enough to fit easily in a briefcase.
Notebook computers use a variety of techniques, known as flat-panel technologies, to produce a lightweight and non-bulky display screen. The quality of notebook display screens varies considerably.
In terms of computing power, modern notebook computers are nearly equivalent to personal computers, They have the same CPUs, memory capacity, and disk drives.
Notebook computers cost about twice as much as equivalent regular-sized computers. Notebook computers come with battery packs that enable you to run them without plugging in.
Tablet PC or slate-shaped mobile computer, equipped with a touch screen type of notebook computer having LCD screen on which the user can write using a special-purpose pen called Stylus .
The handwriting is digitized and can be converted to standard text through handwriting recognition or can be remained as handwritten text. Like PCs Tablet PCs uses keyboard and mouse for input.
The tablet PC relies on digital ink (technology that digitally represents handwriting in its natural form ) technology, where a digitizer is laid under or over an LCD screen to create an electromagnetic field that can capture the movement of the special-purpose pen and record the movement on the LCD screen.
Its effect is like writing on paper with liquid ink.
Personal Digital Assistant (PDA)
Smart cell phones
A portable computer that is small enough to be held in one's hand.
Although it is extremely convenient but still handheld is not replacement of notebook computers.
The most popular hand-held computers are those that are specifically designed to provide PIM (Personal Information Manager) functions, such as a calendar and address book.
Its keyboard is being displayed on screen and stick is used to pick a character.
Personal Digital Assistant
PDA is a handheld lightweight consumer electronic device that looks like a hand-held computer but instead performs specific tasks and can serve as a digital diary, computing, electronic organizer,, entering, storing, and displaying schedules, appointments, addresses, phone numbers, other personal data, telephone/fax, and networking features together,
A typical PDA can function as a cellular phone, fax sender, and personal organizer. Unlike portable computers, most PDAs are pen-based, using a stylus rather than a keyboard for input.
Some PDAs can also react to voice input by using voice recognition technologies.
PDA such as a Palm Pilot is a next-generation Cell Phone which could capable data and voice . Many of these devices now provide the ability to access web content remotely, over wireless networks.
Palmtop Palmtop is a small computer that literally fits in your palm also pocket computers, comparing to full-size computers they work for certain functions such as phone books and calendars. Because of their small size, most palmtop computers do not include disk drives but PCMCIA slots enable you to add disk drives, modems, memory, and other devices. Palmtops are smaller, lightweight with sufficient battery life, palmtops larger and heavier version is called handheld computer. The Palmtop is designed with a small keyboard and a flip-up screen and is more usable to surf the web while you are on the move.
Smart cellphones Smart cell phone is simply a phone with advanced features like e-mail, Internet and e-book reader capabilities and built-in keyboard. In other words, it is a miniature computer that has phone capability smart cell phone is a mobile phone offering advanced capabilities, often with PC-like functionality and can work PC-Mobile handset conversion.
Server is a sort of computer, designed for network based various appliction and provide services to its clients or workstations.
The server is generally used to allow or restrict applications to clients on a network.
Servers require powerful processors, large amount of hard disk drives and memory.
Server of this type is often called middleware server, the function of this server is to meet application and this type of server connect client and host.
Audio/Video servers provide access of online music content using streaming technology.
File Transfer Protocol (FTP) based server makes it possible to move one or more bulky data from one place to an other on the web.
Types of Servers
Chat servers enable a large number of users to exchange text, voice, pics and other online content using real-time capabilities.
One of the most important server of Internet cloud, mail servers send/recieve and store mails using the network of LAN and WAN.
Yahoo, Gmail, Hotmail are the best examples of mail servers.
Proxy server basically designed to provide internet services to its network clients, govt institutions, business points, small networks and cyber cafes are ideal for internet browsing using proxy server.
This is one of the core server is designed to save and provide access to huge databases of an organization, research centre, banks and database institutions.
NADRA have best use database servers.
In networking, environment workstation or client computer connected to a local-area network, its capability is between personal computer and minicomputer
High-speed personal computers are equivalent to low-speed workstations and high-speed workstations is equivalent to minicomputers.
Like personal computers, most workstations are single-user computers. However, workstations are typically linked together to form a local area network but also be used as stand-alone systems.
without a disk drive. The most common operating system for workstations are UNIX and Windows NT.
It is a midsized and mid-range of computer.
In size and power, minicomputers are between workstations and mainframes.
In the past decade, there was little difference between large minicomputers and small mainframes.
Minicomputer is a multiprocessing system capable of supporting from 4 to about 200 users when are in networking environment.
Minicomputers and PCs are ideal home network, mid- range server to serve multiple users.
Mainframes Mainframe is based on the cabinet containing central processor unit or "main frame" in a entire room, it is an other giant computer after the super computer is Mainframe, which can also process millions of instructions per second and capable of accessing billions of data. This type of computer commonly used in big hospitals, air lines reservations companies because its capability to get, manage and retrieve bulk of data. Likewise super computer it is also most expensive and recommended for specials applications.
Nowadays a Mainframe is a very large and expensive computer capable of supporting hundreds, or even thousands, of users simultaneously.
The chief difference between a supercomputer and a mainframe is that a supercomputer channels all its power into executing a few programs as fast as possible, whereas a mainframe uses its power to execute many programs concurrently.
Mainframe you are able to build a large network for several hundred clients. You can process millions of transactions daily with the mainframe because of its high capacity. Most of enterprises such as large organizations, insurance businesses, industry, banking usually use the mainframe for processing and storing enormous amounts of data every day
Super Computer The biggest in size, the most expensive in price than any other is classified and known as super computer. It can process trillions of instructions n seconds, this computer is neither used as a PC in a home nor student in college. This is special purpose computer, most govt. institutions use this type of computer for their different calculations and heavy job, different industries use this huge computer for designing the products.
Supercomputer is a broad term for one of the fastest computers currently available.
It is used in weather forecasting requires a supercomputer. Other uses of supercomputers scientific simulations, (animated) graphics, fluid dynamic calculations, nuclear energy research, electronic design, and analysis of geological data, petrochemical applications.
Hollywood movies use this computer for animation to movies also used in advance weather forecast.
Wearable computers The latest trend in computing is wearable computers possessing email, database, multimedia, calander/schedular are integrted into watches, cell phones, visors and even clothing. When the users hands and other sensory organs are engaged in other activities, wearable computers are of great help in tracking human actions, these computers are consistently in operation as they do not have to be turned on and off and are constantly interacting with the user. Wearable computers are worn on the body parts and they have been applied to areas such as behavioral modeling, health monitoring systems.