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LECTURE TWO. EVOLUTION AND TYPES OF COMPUTERS. Introduction. After having an overview of computer systems, let us now move on to learn how they have evolved over the years, from a computer that filled a whole room to one which can fit in your hand. The History of Computers.

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Lecture two






  • After having an overview of computer systems, let us now move on to learn how they have evolved over the years, from a computer that filled a whole room to one which can fit in your hand.

The history of computers

The History of Computers

  • The first electronic computers were produced around 1940s. This was after a gradual change from the traditional processing aids E.g. abacus, slide rule etc. Some of the saline historical events as concerns the research towards computers origination are described below.

Lecture two


Lecture two

  • In 1614, logarithm as an aid of calculation was invented by a Scottish mathematician known as John Napier, who subsequently invented a rod of bones, the idea which was in use three years later after his logarithm invention and was employed in carrying out multiplications.

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Napier’s Bones

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  • In the year 1620, the slide rule was invented by William Oughtred an English man.

  • In 1623, the idea of using binary numbers to represent e.g. characters, what was described as the binary codes was invented by Francis Bacon.

  • In 1642, the calculating machine, which had both the ability to add and to subtract numbers, was invented by Blaise Pascal.

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Pascal’s calculating machine

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  • In 1671, a calculating machine which had got the capability to multiply and to divide numbers was invented by Gottfried Von Leibniz.

  • At around 1802, a Jacquard Loom was invented by Jacquard. The machine was used to store instructions for weaving on the punched cards. This formed the basis for the programmable computer.

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Jacquard Loom

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  • In 1822 Charles Babbage, a professor of mathematics invented the model for the difference machine, whose design he did not complete but he later in 1834 used the same idea to develop a general purpose calculator, whose design was very close to the design of the computer today. . He is usually referred to as the grandfather of computer science. He built a computer theoretically, but his ideas were too advanced for the available technology.

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Charles Babbage

The grandfather of computers

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  • Between1847–54, George Boole discovered Boolean algebra, whose principles are the basis of today’s computer logic gates used as logical elements.

  • Around Mid 1880s the tabulator machine was discovered by the Herman Hollerith, the machine had the capabilities of detecting data stored in terms of punched holes on the cards. Hollerith’s company later became IBM of today.

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  • Data stored in punched cards or tape must be read and interpreted into an understandable language. His ideas contributed to the invention of punched card readers and paper tape readers used in the first generation of computer systems.

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Hollerith’s Machine

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  • In 1900, the magnetic storage media principles as on e.g. magnetic tapes was discovered by Valdemar Poulson. Magnetized storage is used a lot in computer systems.

  • At around 1906, thermionic valves was invented by the Lee de Forest. The valves were useful in the electronic logics implementation. This were used for internal storage of first generation computers.

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  • In 1937, Automatic Sequence Controlled Calculator (ASCC) was developed by Howard Aiken and IBM. In 1959, Aiken developed punched paper tape, to be used as an input medium.

  • In 1938, ClaudeShannon established how Boolean algebra could be applied in the design of the computer’s logical circuits. This concept is still used in present day computers.

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  • In 1941, the calculating machines, Z3 and Z4 were developed by Konrad Zuse and these machines had the ability to use programs. Lady Ada is claimed to possibly be the first programmer. Ada a programming language was named after her in honor of her contribution to computer programming concept.

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  • Aiken worked out a plan, to set mechanical calculators to work on mathematical problems in control sequences. He set up a project to develop the necessary equipment and with the support of International Business Machines Corporation and Harvard University, and assistance from four co-workers from IBM, he built the first computer.

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  • This machine, called International Business Machines Automatic Sequence, Controlled Calculator, and also known as the Harvard Mark 1 computer was presented to Harvard University in August 1944. It was the firstinformation processing machine and it was electrically powered.

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Aiken’s Machine

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  • In 1946, Electronic Numerical Integrator and Calculator (ENIAC) was in use, developed by Presper Eckert and John Mauchly. The machine used valves and consumed a lot of power. It was water cooled. It was huge, taking up the walls of a room, 20 x 40 feet in size. This was the first electronic computer.

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Figure ENIAC

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  • In 1946, Von Neumann gave a report on the design which forms the basis of today's computer. He demonstrated that one could encode instruction to the machine, in the same language used for the data it processed. This brilliant demonstration made it possible to mix instructions and data in the program as both could also be stored in the computer.

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John Von Neumann’s Machine

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  • All of the above had contribution to the present day computer which is being improved on as the time goes by. Their ideas are still being researched and used in computer systems.

Computer generations

Computer Generations

  • Following the development of the first electronic computer in 1946, the historical events in respect of computer development are not considered individually or in terms of individual years but in classifications of durations of periods known as “generations”. A generation groups computers of like technological characteristics.

Lecture two

  • The transition from one generation to another was, and is influenced by the amount of research towards further development of the computers, and the related facilities and concepts.

  • We shall now describe computer generations:

First generation computers

First generation Computers

  • These were the earliest time computers, which were in use from around the mid 1950’s to late 1950,s. They used big physical devices in their circuitry and hence were very big in their physical size. Their circuits incorporated the thermionic valves, a non solid state electronic device as a major logic element.

Lecture two

These computers

  • Consumed a lot of power generating a lot of heat and hence non-reliable as the circuitry components were prone to failure.

  • They had limited internal memory which was based on the use of delay lines

  • The processor worked at slow speed as compared to the speeds of the computers of today.

Lecture two

  • Their design was based on the John Von Neumann’s recommendations.

  • Examples of the first generation computers are UNIVAC and a commercial computer known as Lyon’s Electronic Office (LEO).

Second generation computers

Second Generation Computers

  • These were computers of the closing of the 1950s to the early1960s which used transistors.

  • The transistors are relatively smaller than valves and consume comparatively less power and therefore, the resulting computers were more reliable and comparatively small in size.

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  • The transistors were based on the solid-state technology, where the electric pulses were not to flow through a vacuum as in the case of the thermionic valves of the first generation computers.

  • The second-generation computers’ internal storage was higher than those of the first generation computers. The core memory replaced the delay lines and the magnetic drums, the internal memory of the first generation computers.

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  • The second-generation processors operated at a comparatively higher speed than those of the first generation computers.

  • The design of these second generation computers/processor was on a family basis; that is one family of computers had a set of related technological characteristics.

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  • These computers had programming languages whose vocabularies are close to the human language, specifically the English language. Examples of the second-generation computers include IBM 300 Series and ATLAS.

Third generation computers

Third Generation Computers

  • The computers of this generation came into being towards the mid 60’s and they used integrated circuits to replace the second-generation computer physical transistors.

  • The integrated circuits combine several physical electronic components within a small crystal called the silicon chip (IC- Integrated Circuit).

Lecture two

  • The resulting computer was reduced in sizes as compared to the second-generation computers.

  • The small circuitry that resulted, improved the processing speed for pulses as data pulses could flow faster from one module to another as compared to the flow within the larger circuits, where they travel considerable distances.

Lecture two

  • The third generation computers had higher main memory capacity..

  • These computers were of increased processing power as compared to the second-generation computers, and therefore, had the capability of holding more than one set of instructions (programs) – Multiprogramming.

  • Could support more than one user

Lecture two

  • These computers had the capability to support communication facilities i.e. remote communication facilities.

  • Users could be in remote locations or the same location

  • Examples of such computers are ICL 1900 Series, IBM 360.

Fourth generation computers

Fourth Generation Computers

  • The fourth generation computers resulted from a modification of the third generation computer’s technology. The design of this computer is based on Large Scale Integration (LSI) of circuitry and Very Large Scale Integration (VLSI) of circuitry.

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  • This generation marked the origin of mini computers in use today.

  • The design of the fifth generation computers was based on the VLSI technology that gave rise to PCs.

  • The microcomputers are usually described as PCs or stand-alone or desk top computers because they were primarily to serve a single person at a time.

Fifth generation computers

Fifth Generation Computers

  • The fifth generation is still a state of the art of technology that relies on predictions and further technological refinements.

Trends in computer technology

Trends in Computer Technology

The trend in the computer’s technological revolution can be summarized as follows:

  • Continual decrease in computer size

  • Improved speed and power of processing

  • Decrease in computer’s and its related facilities cost

  • Increase in the number of components per circuit (IC).

Computer classifications

Computer Classifications

  • Because of the variations in characteristics of computers, computers can be categorized by:

    (a) Data Manipulated

  • Analog computers

  • Digital computers

  • Hybrid computers

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(b) The purpose for which they are designed :-

  • General purpose computers

  • Special purpose computers

  • Dedicated Computers

    (c) The basis of price, size and capabilities

  • Main frame computers

  • Mini computers

  • Micro computers

  • Personal computers

Classification of computers by the types of data manipulated

Classification of Computers by the Types of Data Manipulated

  • Analog computers perform arithmetic operations and logical comparisons by measuring changes in physical magnitudes such as, electronic voltage, pressure changes, and temperature changes.

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  • The application of analog computers is confined to specialized areas as in scientific or engineering experiments, manufacturing processes and military weapons.

  • The examples of analogue devices include thermometer and car speedometer.

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  • The output from the system may be in the form of a graph produced by a plotting pen or a trace on a cathode ray tube. Its output signals can be used directly to control the operation of some other machine or process.

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Digital computers are the most commonly used type of computers. Their arithmetic operations and logical comparisons are based on digits (1s and 0s) and on other characters that have been numerically coded.

These computers can process both numeric and alphabetic or alphanumeric data. Memory sizes determines capability

Lecture two

  • These types of computers are used in a wider cross section of the application areas such as scientific, industrial and most of the other computer based data processing applications. The digital computer also has a unique ability, and that is, storing large quantities of data.

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  • Hybrid computers are designed by interconnecting the digital computer and analog computers’ element directly into one processor, using a suitable interfacing circuitry. That is, both the digital and analog features are built within the same computer/processor.

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  • Because of their capabilities they are more expensive. For example in a hospital ICU unit, analogue devices may measure a patient’s heart function, temperature and other vital signs. These measurements may then be converted into numbers and supplied to a digital device which may send an immediate signal if any abnormal readings are detected.

Lecture two

  • Special Purpose Computers are digital computers are designed to carry out special processing tasks in one or more applications.

  • For example, in a computer network, a special type computer known as the Front End Processor (FEP) may be used to specialize in the work of network control,

Lecture two

  • General Purpose Computers are digital computers designed to be used in a variety of application environments as required. This capability of the computers is made possible by passing into the computer the relevant sets of instructions, to be used by the computer to carry out the desired different processing tasks at any given time.

Lecture two

  • Dedicated Computers are general-purpose computers that are committed to some processing tasks. They are nevertheless capable of a variety of tasks. A general-purpose computer, for example, can be dedicated to carry out airline reservation.

Classification of computers based on price size and capabilities

Classification of Computers Based On Price, Size and Capabilities

  • In terms of capacity, price and performance criteria, computers can be further categorized as follows:

  • Mainframe computers

  • Minicomputers

  • Microcomputers

  • Personal computers

Lecture two

  • Mainframe computers are most expensive of all the computers and are very big in size and offer the maximum computing power. A large number of peripherals can be attached to them. They are generally used in large networks of computers with the mainframe being the nodal point of the network. Smaller computers are included in the network.

Lecture two

  • A typical application of mainframes is found in the airline reservation systems. The airlines have a mainframe computer at their head office where information of all the flights is stored. Smaller computers, installed at the booking offices, are attached to the central data bank so that up-to-date information of all flights is always available.

Lecture two

  • They can accept and transfer data from input/output devices at the rate of millions of bytes per second.

  • These are big general purpose computers capable of handling all kinds of problems whether scientific or commercial.

  • They can accept all types of computer languages.

  • They can support a large number of terminals.

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  • They usually have instruction sets that give them the flexibility to operate automatically.

  • They have large on-line secondary capacities and can support a number and variety of peripheral devices

  • They routinely have high speed cache memory, which enables them to process applications faster than mini or micro computers

Lecture two

Example of a mainframe computer

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  • The minicomputers are medium sized computers. They support average internal and backing storage. Their storage capabilities both internal and external are comparatively higher than the microcomputers but lower than the mainframe.

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  • They are more powerful and reliable than the microcomputers though slower than the mainframes. They are more costly than the micros but cheaper than the mainframes.

  • Minicomputers are used mainly in medium scale businesses

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Mini Computer

Lecture two

  • Microcomputers are computers of advanced technology that became available in the late 1970’s. The advent of micro computers brought computers within reach of even the small businesses. The microcomputers are the most common form of computers in offices today. They include the desktop, personal or standalone systems.

Lecture two

  • The micro computers are the smallest of the three computer classes. Their design is based on large scale circuit integration that confines several physical components to smaller elements, the size of a thumb.

  • Their internal memory is smaller than the mini computers and the mainframe computers.

Lecture two

  • The micro computer configuration typically includes: A monitor, a keyboard, Winchester disk (hard disk), a mouse, a printer, a diskette drive and an optical disk drive. Can be connected to larger computer.

  • Note: this configuration is changing and, therefore making the micro computer very powerful. Some of them are able to support more than one user.

Lecture two

Micro Computer

Generations of programming languages

Generations of Programming Languages

  • We have seen how computers have developed over the years, but one thing we have to keep in mind is that, computers are “dumb” machines. They can only do what they are instructed to do. Instructions that are given to the computer are called programs and they are given in different languages.

Machine languages first generation language

Machine Languages (First Generation Language)

  • Machine language is a programming language in which the instructions are in binary code, or machine code. Each instruction corresponds directly to a hardware facility on the machine for which it is written. No further interpretation is necessary

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  • This language is machine dependent, meaning that each computer has its own machine language.

  • This is the most basic level of programming language. In early stages of computer development, all instructions had to be written using this language.

Assembly languages second generation languages

Assembly Languages (Second Generation Languages)

  • Assembly languages are low-level languages. They were developed to reduce the difficulties in writing machine language. They are machine oriented meaning that they are close to machine vocabulary rather than human vocabulary.

Lecture two

  • Each instruction resembles a machine instruction; mnemonic codes are used instead of machine code.

  • Assembly languages must be translated to machine language before use by the computer. A manufacturer usually avails the language.

  • Features of these languages differ from computer to computer.

High level languages third generation languages

High-Level languages (Third Generation Languages)

  • The development of low level languages was a great achievement, but was still dependent on the machine, meaning that it could not be imported to different machines. Thus, there was a need for high level for high level languages.

Lecture two

  • High-level languages are machine independent and are problem-oriented languages. They reflect the type of problem to be solved rather than the features of the machine.

  • Machine independence means that in principle it should be possible to make the same high-level languages run on different machines. Programs should also be portable. In this instance:

Lecture two

  • Users can change computer without the need to rewritten programs.

  • Users of different computers may be able to share or exchange programs and reduces costs.

  • An organization producing software for sale can sell the same program to users of different computers without the need to rewrite the programs for each type of computer.

Very high level languages fourth generation languages

Very High-level Languages (Fourth Generation Languages)

  • 4GLs are user oriented rather than problem oriented. They are easy to learn and understand because they are user based. The languages syntax (grammar) is natural, near English. It uses menus and prompts to guide a non-specialist to retrieve data at ease.

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  • Very little training is essential before these language’s programs can be used or developed. They continue to grow. An example is Microsoft access.

    Fifth Generation Languages

  • These languages are still in a state of development. They are not famous in the market and to programmers.



  • A translator is a program that converts statements written in one language, to another language. There are three types of translators:-

  • Assembler. A languagethat translates assembly language into machine code.

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  • Compiler. A program that translates high level language into machine code

  • Interpreter. A program that translates an instruction into an object code and works on it immediately.



  • Who is the father/grandfather of computers?

  • Francis Bacon discovered binary numbers, why is this invention useful in today’s electronic devices?

  • There are two first computers, Aikens MARK I and ENIAC by Eckert an Mauchly, what is the difference between the two computers?

  • Why are fouth generation computers smaller and faster than the earlier computers?

  • Describe a hybrid computer.

  • What is a machine language?

  • Classify computers by their price, size and capability

Lecture two


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