When more than one thing Is needed to work together before an action can take place, we say we have a system. The computer needs several things before it can be used to solve problems. Therefore, we say the computer is a system. We may have systems around us even In our body. How we eat or what happens to the food we eat is a system. This is called the Digestive System. We need mouth, tongue, teeth and stomach for us to make good use of the food we eat.

Originally, the term "computer" referred to a person who performed numerical calculations (a unman computer), often with the aid of a mechanical calculating device. Automated calculation and that of programmability. Examples of early mechanical calculating devices included the abacus, the slide rule and the Antiheroes mechanism (which dates from about 150-100 SC). The hero of Alexandria (c. 10-70 AD) built a mechanical theater which performed a play lasting 10 minutes and was operated by a complex system of ropes and drums that might be considered to be a means of deciding which parts of the mechanism performed which actions and when.

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This is the essence of programmability. The "castle clock", an astronomical clock invented by Al-Izard in 1206, is considered to be the earliest programmable analog computer. It displayed the zodiac, the solar and lunar orbits, a crescent moon-shaped pointer traveling across a gateway causing automatic doors to open every hour, and five robotic musicians that played music when struck by levers operated by a camshaft attached to a water wheel. The length of day and night could be re-programmed every day in order to account for the changing lengths of day and night throughout the year. ND of the middle Ages saw a re-invigoration of European mathematics and engineering, and Wilhelm Churchyard's 1623 device was the first of a number of mechanical calculators constructed by European engineers. However, none of those devices fit the modern definition of a computer because they could not be programmed. In 1801 , Joseph Marie Jacquard made an improvement to the textile loom that used a series of punched paper cards as a template to allow his loom to weave intricate patterns automatically.

The resulting Jacquard loom was an important step in the development of computers because the use of punched cards to define woven tatters can be viewed as an early, albeit limited, form of programmability. It was the fusion of automatic calculation with programmability that produced the first recognizable computers. In 1837, Charles Babbage was the first to conceptualize and design a fully programmable mechanical computer that he called "The Analytical Engine". Due to limited finances, and an inability to resist continuously changing with the design, Babbage never actually built his Analytical Engine.

Large-scale automated data processing of punched cards was performed for the U. S. Census in 1890 by tabulating machines designed by Herman Hollering and manufactured by the Computing Tabulating Recording Corporation, which later became MM. By the end of the 19th century a number of technologies that would later prove useful in the realization of practical computers had begun to appear: the punched card, Boolean algebra, the vacuum tube (thermion valve) and the teleprompter.

During the first half of the 20th century, many scientific computing needs were met by increasingly sophisticated analog computers, which used a direct mechanical or programmable and generally lacked the versatility and accuracy of modern digital computers. A succession of steadily more powerful and flexible computing devices were constructed in the sass and sass, gradually adding the key features that are seen in modern computers.

The use of digital electronics (largely invented by Claude Shannon in 1937) and more flexible programmability were vitally important steps, but defining one point along this road as "the first digital electronic computer" is difficult Notable achievements include: 0 DEEDS was one of the first computers to implement the stored program architecture of von Neumann. 0 Conrad Use's electromechanical "Z machines". The OZ (1941) was the first working machine featuring binary arithmetic, including floating point arithmetic and a measure of programmability.

In 1998 the OZ was proved to be Turing complete, therefore being the world's first operational computer. The nonprogrammable TANSTAAFL-Berry Computer (1941) which used vacuum tube based computation, binary numbers, and regenerative capacitor memory. 0 The secret British Colossus computers (1943) which had limited programmability but demonstrated that a device using thousands of tubes could be reasonably reliable and electronically reprogrammable. It was used for breaking German wartime codes. 0 The Harvard Mark I (1944), a large-scale electromechanical computer with limited programmability. The U. S.

Army's Ballistics Research Laboratory invented Electronic Numerical Integrator and Calculator, MANIAC (1946), which used decimal arithmetic and is sometimes called the first general purpose electronic computer (since Conrad Use's OZ of 1941 used electromagnets instead of electronics). Initially, however, MANIAC had an inflexible architecture which was not flexible essentially requiring rewiring to change its programming. Several developers of MANIAC, recognizing its flaws, came up with a far more flexible and elegant design, which came to be known as the "stored program architecture" or Von Neumann architecture.

This design was first formally described by John von Neumann in the paper First Draft off Report on the ADVANCE, distributed in 1945. A number of projects to develop computers based on the stored-program architecture commenced around this time, the first of these being completed in Great Britain. The first to demonstrate its workability was the Manchester Small-Scale Experimental Machine (SEEM or "Baby"), while the DEEDS, completed a ear after SEEM, was the first practical implementation of the stored program design.

Shortly thereafter, the machine originally described by von Newsman's paper-? Nearly all modern computers implement some form of the stored-program architecture, making it the single trait by which the word "computer" is now defined. While the technologies used in computers have changed dramatically since the first electronic, general-purpose computers of the sass, most still use the von Neumann architecture. Microprocessors are miniaturized devices that often implement stored program central processing units (JPL's). Hat used vacuum tubes as their electronic elements were in use throughout the sass.

Vacuum tube electronics was largely replaced in the sass by transistor-based electronics, which are smaller, faster, cheaper to produce, require less power, and are more reliable. In the sass, integrated circuit technology and the subsequent creation of microprocessors, such as the Intel 4004, further decreased size and cost and further increased speed and reliability of computers. By the sass, computers became sufficiently small and cheap to replace simple mechanical controls in domestic appliances such as washing machines. The sass also witnessed availabilities of home computers and the now common personal computer.

With the evolution of the Internet, personal computers are becoming as common as the television and the telephone in the household. In 2005, Nooks started to call its top- line smart phones of the N-series "multimedia computers" and after the launch of the Apple Phone in 2007, many are now starting to add the smart phone category among "real" computers. In 2008, if the category of smartness is included in the numbers of computers in the world, the biggest computer maker by units sold is no longer Hewlett-Packard (HP), but Nooks. 3 CLASSIFICATIONS OF COMPUTERS One of the ways in which computers are classified is by type of data processed is broadly referred to as types of computers. Statisticians generally classify data collected by counting as discrete data e. G. Head count, number of Mangoes etc. Similarly, data collected through measurement are called continuous data. Examples are temperature, height, weight etc. This concept will help us to understand the types of computers. Computers are also classified by their different generations or by their size, or by the different purposes for which they are meant. . 3. CLASSIFICATION BY TYPE OF DATA PROCESSED I. I Analog Computers I Analog computers are those that represent data in a continuous manner using physical variables such as pressure, temperature etc. An example is the analog smooth curves or graphs from which information can be read. These computers are less accurate than digital output since their accuracy depends on the user or reader of such output. These classes of computers are used for scientific/ engineering purposes and are not concerned with commercial data processing.

A good example of this class of computer is the computer used in hospitals for assuring blood pressure of patients, also a filling station gasoline pumps work purely on analog processes. The volume of fuel pumped out is converted into two measurements (I) price to the nearest kobo, and (it) volume of fuel to the nearest liter. Other simple devices are the slide-rule, and the car speedometer. It. I Digital Computers I These are computers that represent data in discrete or discontinuous manner using binary system. A digital watch is an example of a digital device. The output from digital computers are usually in the form of discrete values.

This class of amputees are commonly found in the business environments, and they include Desk calculators, Adding machines, and most of the computers we have around (MM, BBC, Radio Shack Personal Computers (PC), Laptops, Desktops etc. Iii. I Hybrid Computers I As the name implies, this class of computers combines the features of both digital and analog computers. Their outputs could be in the form of discrete or continuous value or a combination of both. This class of computers is commonly found in highly scientific environments. Example is an electronic calculating scales used in food stores.

Of these three; digital computers are the most common, since they lend themselves to use in business, scientific and even home environments. 6. 3. 2 CLASSIFICATION BY GENERATIONS The classifications of computers sometime discussed to in reference to the different generations of computing devices. Each generation of computer is characterized by a major technological development that fundamentally changed the way computers operate, resulting in increasingly smaller, cheaper, and more powerful and more efficient and reliable devices. Below is a summary of each generation and the developments that led to the current vices that we use today.

The first computers used vacuum tubes for circuitry and magnetic drums for memory, and were often enormous, taking up entire rooms. They were very expensive to operate and in addition to using a great deal of electricity, generated a lot of heat, which was often the cause of malfunctions. First generation computers relied on machine language, the lowest-level programming language understood by computers, to perform operations, and they could only solve one problem at a time. Input was based on punched cards and paper tape, and output was displayed on printouts.

The UNIVAC and MANIAC computers are examples of first-generation computing devices. The UNIVAC was the first commercial computer delivered to a business client, the U. S. Census Bureau in 1951. (it) Second Generation (1956-1963): Transistors Transistors replaced vacuum tubes and ushered in the second generation of computers. The transistor was invented in 1947 but did not see widespread use in computers until the late ass. The transistor was far superior to the vacuum tube, allowing computers to become smaller, faster, cheaper, more energy-efficient and more reliable than their first-generation predecessors.

Though the transistor still generated a great deal of heat that subjected the computer to damage, it was a vast improvement over the vacuum tube. Second-generation computers still relied on punched cards for input and printouts for output. Second-generation computers moved from cryptic binary machine language to symbolic, or assembly, languages, which allowed programmers to specify instructions in words. High-level programming languages were also being developed at this time, such as early versions of COBOL and FORTRAN.

These were also the first computers that stored their instructions in their memory, which moved from a genetic drum to magnetic core technology. The first computers of this generation were developed for the atomic energy industry. (iii) Third Generation (1964-1971): Integrated Circuits The development of the integrated circuit was the hallmark of the third generation of computers. Transistors were miniaturized and placed on silicon chips, called semiconductors, which drastically increased the speed and efficiency of Instead of punched cards and printouts, users interacted with third generation computers through keyboards and monitors.

These were interfaced with an time with a central program that monitored he memory. Computers for the first time became accessible to many because they were smaller and cheaper than their predecessors. (v) Fourth Generation (1971 -Present): Microprocessors The microprocessor brought the fourth generation of computers, as it became possible to build thousands of integrated circuits were built onto a single silicon chip. What in the first generation filled an entire room could now fit in the palm of the hand.

The Intel 4004 chip, developed in 1971, located all the components of the computer - from the central processing unit and memory to input/output controls - on a single chip. In 1981 IBM introduced its first computer for the home user, and in 1984 Apple introduced the Macintosh. Microprocessors also moved out of the realm of desktop computers and into many areas of life as more and more everyday products began to use microprocessors. As these small computers became more powerful, they could be linked together to form networks, which eventually led to the development of the Internet.

Fourth generation computers also saw the development of Graphical User Interface (GU'), the mouse and handheld devices. (v) Fifth Generation - Present and Beyond: Artificial Intelligence Fifth generation computing devices, based on artificial intelligence, are still in development, though there are some applications, such as voice recognition, that are already being used today. The use of parallel processing and superconductors is helping to make artificial intelligence a reality. Quantum computation and molecular and nanotechnology will radically change the face of computers in years to come.

The goal of fifth-generation computing is to develop devices that respond to natural language input and are capable of learning and self organization. 6. 3. 3 CLASSIFICATION BY SIZE What are the different types of computers? Different types of computer systems are nowadays available for different purposes according to the user needs. When you'll have to order yours or even to build it, you should first define the expected use of your computer. This step will help you to describe the basic capabilities and know the costs of Summary of classifications of computers. I)l Personal computers or Microcomputers I Microcomputers are built to be used by one person. In fact when you talk about personal computers or its common acronym PC, you always mean microcomputers. For surfing the web, playing games or music, editing and many there tasks... You ordinarily use personal computers either at school, at home or at business. Personal computers are in two (2) major categories: desktop and laptop. If you opt for a desktop computer you have to set it up in a permanent location. Fortunately you are able to choose your preferred sizes such as a mint, mid or full tower.

You should then add many other devices to complete it such as keyboard, mouse and monitor which can be a Cathode Ray Tube (CRT) or Liquid Crystal Display (LCD). (ii)l Workstations and Servers I If you need a high-end micro computer you should go for a workstation. This type f computer is recommended if you are carrying out game development, scientific calculations, engineering or AD graphics. It is faster than the common personal computer and can be used as a server if you need to set up a network client. The server is generally used for the purpose of allowing many users to work together over a network.

Servers require powerful processors, large amount of hard disk drives and random access memory (RAM). (iii)l Mobile Computers I If you prefer the laptop you'll go for the mobile or portable system. Your notebook, a common name of laptop, has the advantage to have all the parts built gather. The notebook has the same computing power as the desktop machine but it is lightweight enough as to be portable. The mobile computer is relatively more expensive because it costs more to design the small components. For greater portability. A handheld micro computer is now a common option.

To manage your phone book, diary or to taking notes . Etc a Personal Digital You can also use the Palmtop, a tinier laptop, for the same purposes and even more. The Palmtop is designed with a small keyboard and a flip-up screen and is useful for surfing the web while you are on the move. (iv)l Mini Computers I These are medium-sized computers that usually have several terminals for input and output, several disk drives and sometimes tape drives for data storage. Minicomputers have greater storage capacity and are faster in speed than microcomputers.

Most often, minicomputers can process several programs at a time and can be used by several people simultaneously. Small and medium-sized business also uses minicomputer for their data processing need. (v) Mainframe Computers: Mainframe computers have many terminals and several disk and tape drives. The components of mainframe computers have greater outrage capacity and are faster than those of minicomputers. Mainframe computers can process numerous programs concurrently and can be used by medium and large sized business for their data processing needs.

For example the network support for Automatic Teller Machines (Tams). (v') Super Computers: These are the most powerful and most expensive computers. They are designed for very fast processing speeds. Although they have some fewer terminals and their processors can operate much faster, supercomputers are mainly used for complex mathematical calculations such as those needed in scientific research, or space exploration of their complexity and cert.. CLASSIFICATION BY PURPOSE I I. Special Purpose computers I These are computers designed to carry out specific tasks.

They have in-built programs which are stored in a part of the main memory called Read-only Memory (ROOM). The content of this part of the memory can be accessed and executed by the computer, but cannot be modified by the programmer or the user. Thus, the operations that can be carried out by this type of computer are predetermined at the time of manufacture. The computer cannot be used for any other purpose. Microcomputers (small computers) are so inexpensive however; that we can afford to use them to perform specific functions such as telling the time, it.

I General Purpose Computer I These are computers that are not specifically designed or built for specific Jobs. They solve various kinds of problems depending on the program or software loaded into them. Their main memory is typically Random Access Memory (RAM) - a temporary storage that looses its contents when the computer is switched off. It is easy to change the contents of RAM, substituting one program for another and this is what makes them general-purpose computers. Most microcomputers or PC's are general purpose computers.