Basic Computer Organization

 A computer is an electronic device, which can input data, process it, store the intermediate results and display output. All computer systems perform the following five basic operations: 

1. Input. The process of entering data and instructions into the computer system. 
2. Storing. Saving data and instruction for future use in the memory of a computer is called as storage. 
3. Processing. Performing arithmetic and logical operations on the data to produce some information is called as processing. 
4. Output. The process of producing the result on paper or on screen is called as outputting. 
5. Controlling. Directing the manner and sequence in which all of the above operations are performed. 

The basic organization of a computer can be very easily depicted with a block diagram. The solid lines indicate the flow of data and information and the dotted lines represent the control exercised by the control unit. It displays five major building blocks or functional units, of a digital computer system. These five units correspond to the five operations performed by all computer systems. 

Input Unit

Data and instructions must enter the computer system before any computation can be performed on the supplied data. This task is performed by the input unit, which links the external environment with the computer system. Data and instructions enter input units in forms that depend upon the particular device used. For example, data is entered from a keyboard in a manner similar to typing, and this differs from the way in which data is entered through a card reader, which is another type of input device. However, regardless of the form in which they receive their inputs, all input devices must provide a computer with data that are transformed into the binary codes that the primary memory of a computer is designed to accept. Units called input devices accomplish this transformation. Input interfaces are designed to match the unique physical or electrical characteristics of input devices to the requirements of the computer system.

Functions of an input unit 

1. It accepts or reads the list of instructions and data from the outside world. 
2. It converts these instructions and data in computer acceptable form. 
3. It supplies the converted instructions and data to the computer system for further processing. 

Output unit 

The job of an output unit is to supply the information and result of computation to the outside world. Thus it links the computer with the external environment. As computers work with binary code, the results produced are also in the binary form. Hence, before supplying the results to the outside world, it must be converted to human acceptable form. Units called output interfaces accomplish this task. Output interfaces are designed to match the unique physical and electrical characteristics of output devices to the requirements of the external environment. 

Storage unit

The data and instructions that are entered into the computer system through input units have to be stored inside the computer before the actual processing starts. Similarly, the results produced by the computer after processing must also be kept somewhere inside the computer system before being passed ion the output units. Moreover, the intermediate results produced by the computer must also be preserved for ongoing processing. The storage unit or the primary /main storage of a computer system is designed to cater to the needs of storage. It provides space for storing data and instructions, space for intermediate results, and also space for the final results. 

Arithmetic and logic unit

The Arithmetic and logic unit (ALU) of a computer system is the place where the actual execution of these instructions takes place during the processing operation. To be more precise, all calculations are performed and all decisions (comparisons) are made in the ALU. The data and instructions, stored in the primary storage prior to processing, are transformed as and when needed to the ALU where processing takes place. No processing is done in the primary storage unit. Intermediate results generated in the ALU are temporarily transferred back to the primary storage until needed at a later time. Data may thus move many times before the processing is over. After the completion or processing, the final results, which are stored in the storage unit, are released to an output device.

The type and number of arithmetic and logic operations that a computer can perform is determined by the engineering design of the ALU. However, almost all ALU's are designed to perform the four basic arithmetic operations - add, subtract, multiply, divide and logic operation or comparison such as Less than, greater than, equal to, not equal to etc. 

Control unit

Some questions may arise in your mind.

How does the input device know that it is time for it to feed data into the storage unit? How does the ALU know what should be done with the data once they are received? And how is it that only the final results are sent to the output device and not the intermediate result? All this is possible because of the control unit of the computer system.

• By selecting, interpreting, and seeing to the execution of the program instructions, the control unit is able to maintain order and direct the operation of the entire system. 
• Although, it does not perform any actual processing on the data, the control unit acts as a central nervous system for the other components of the computer.
• It manages and coordinates the entire computer system. 
• It obtains instructions from the program stored in main memory, interprets the instructions, and issues signals that cause other units of the system to execute them. 

Central processing unit

The control unit and the arithmetic logic unit are jointly known as the central processing unit (CPU). The CPU is the brain of any computer system. In a human body, the brain takes all major decisions. Similarly, in a computer all major calculations and decisions are made inside the CPU and the CPU is responsible for activating and controlling the operations of other units of a computer system.

Computer as a system

A system is a group of integrated parts that have common purpose of achieving some goal. So is a computer, which is made up of integrated components (Input, Output devices, storage unit, CPU) that work together to perform some task or goal. 

Points to Remember

• A computer is an electronic device, which can input data, process it, store the intermediate results and display output. Input. The process of entering data and instructions into the computer system. 
• Storing. Saving data and instruction for future use in the memory of a computer is called as storage. 
• Processing. Performing arithmetic and logical operations on the data to produce some information is called as processing.
• Output. The process of producing the result on paper or on screen is called as outputting. 
• Controlling. Directing the manner and sequence in which all of the above operations are performed. 
• Data and instructions must enter the computer system before any computation can be performed on the supplied data. This task is performed by the input unit, which links the external environment with the computer system. 
• The job of an output unit is to supply the information and result of computation to the outside world. 
• The storage unit or the primary /main storage of a computer system is designed to cater to the needs of storage. It provides space for storing data and instructions, space for intermediate results, and also space for the final results. 
• The Arithmetic and logic unit (ALU) of a computer system is the place where the actual execution of these instructions takes place during the processing operation. 
• The control unit and the arithmetic logic unit are jointly known as the central processing unit (CPU). 
• A system is a group of integrated parts that have common purpose of achieving some goal.

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Categories of Computer

Four categories of computer 

Micro computer 

Micro computers are sometimes called laptop computers," "personal computers" or business microcomputers”. Major micro computer manufacturers include Apple, AT&T, Commodore, Compaq, IBM and Tandy/Radio shack. The most important characteristic of a microcomputer is its low price. However extended memory and hard disks can make the cost high.

A typical microcomputer is operated by a single person- hence the term personal computer or PC. However, most micro computers can operate either as independent computers in "stand alone mode" or an intelligent terminals in "network mode". In stand alone, the microcomputer runs software programs that process data independently. In network mode, the micro enables user to communicate with larger computers and also with each other.

Mini computer

Mini computers are typically multi-user systems, sometimes supporting more than 500 online terminals. Generally, the proceeding speeds and related capabilities of minicomputers exceed those of microcomputers, and more peripheral devices can be attached to them.

Mini computers tends to have more sophisticated operating systems than microcomputers and can usually be programmed in a wider variety of programming languages.

Mainframe computers

Beyond mini, we have mainframes, which are fully configured computers intended for substantial, high volume data processing. Mainframe manufacturers include IBM, CDC etc. Mainframe computers have large primary memory, which usually exceed several millions characters. They have very powerful processors, which can process several million instructions per second. Substantial amount of peripherals can be attached to the computer. These computers can support · thousands of online terminals at once. Mainframe computers are purchased as host computers -i.e., computers that serve as central receiving and switching computer in regional and national computer networks.

Super computers

The largest mainframes are called super computers. They have huge primary memory (measured in hundreds of millions of locations) and the most advanced processing capabilities. Super computers are typically designed with state-of-art computer architecture, including unique cooling systems to dissipate internal heat buildup and the ability to execute programs instructions concurrently instead of sequentially. Prices of super computers can exceed lakhs. Customers include, the national weather service, oil companies, military and aerospace firms.

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Computer Generations

"Generation" in computer talk is a step in technology. It provides a framework for the growth of the computer industry. Originally, the term "generation" was used to distinguish between varying hardware technologies.

First Generation (1942-1955)

First generation machines were invented with the invention of vacuum tubes. A vacuum tube was a fragile glass device that could control and amplify electronic signals. These vacuum tube computers are referred to as first generation computers.

Advantages

1. Vacuum tubes were the only electronic components available those days.
2. Vacuum tube technology made possible the advent of electronic digital computers.
3. These computers were the fastest calculating devices of their time. They could perform computations in milliseconds.

Disadvantages

1. Too bulky in size.
2. Unreliable
3. Thousands of vacuum tubes that were used emitted large amount of heat and burnt out frequently.
4. Air conditioning required.
5. Prone to constant hardware failure.
6. Constant maintenance required.
7. Non-portable.
8. Manual assembly of individual components into functioning unit required.
9. Commercial production was difficult and costly.
10. Limited commercial use.

Second Generation (1955 - 1964)

The transistor, a smaller and more reliable successor to the vacuum tube, was invented in 1947. However, computers that used transistors were not produced in quantity until over a decade later. The second generation emerged with transistors being the brain of the computer.

With both the first and the second-generation computers, the basic component was a discrete or separate entity. The many thousands of individual components had to be assembled by hand into function circuits. The manual assembly of individual components and the cost of labor involved at this assembly stage made the commercial production of these computers difficult and costly.

Advantages

1. Smaller in size as compared to first generation computers. 
2. More reliable 
3. Less heat generated. 
4. These computers were able to reduce computational times from milliseconds to microseconds. 
5. Less prone to hardware failures. 
6. Better portability.
7. Wider commercial use. 

Disadvantages

1. Air-conditioning required. 
2. Frequent maintenance required. 
3. Manual assembly of individual components into a functioning unit was required. 
4. Commercial production was difficult and costly. 

Third generation (1964-1975)

Advances in electronics technology continued and the advent of "microelectronics" technology made it possible to integrate large number of circuit elements into very small (less than 5mm square) surface of silicon known as "chips". This new technology was called "integrated chips" (ICs). The third generation was based on IC technology and the computer that was designed with the use of integrated circuits was called third generation computers, 

Advantages 

1. Smaller in size as compared to previous generation computers.
2. Even more reliable than second-generation computers. 
3. Even lower heat generated than second generation computers. 
4. These computers were able to reduce computational times from microseconds to nanoseconds. 
5. Maintenance cost is low because hardware failure is rare. 
6. Easily portable.
7. Totally general purpose.
8. Less power requirement than previous generation computers, 
9. Manual assembly of individual components into a functioning unit was not required. 
10. Commercial production was cheaper and easier. 

Disadvantages

1. Air conditioning required in many cases. 
2. Highly sophisticated technology required for the manufacture of IC chips. 

Fourth Generation (1975 onwards) - 89

Initially, the integrated circuits contained only about ten to twenty components. This technology was named small-scale integration (SSI). Later, with the advancement in technology for manufacturing ICs, it became possible to integrate upped a hundred components on a single chip. This technology came to be known as medium scale integration (MSI). Then came the era of (LSI) large-scale integration when it was possible to integrate over 30,000 components onto a single chip. Efforts is still on for further miniaturization and it is expected that more than one million components will be integrated on a single chip known as (VLSI) very large scale integration.)

A fourth generation computer, which is what we have now, has LSI chips as its brain. It is LSI technology, which has led to the development of very small but extremely powerful computers. It was the start of a social revolution. A whole computer circuit was soon available on a single chip, the size of a postage stamp. Overnight computers became incredibly compact. They became inexpensive to make and suddenly it became possible for anyone and everyone to own a computer.

Advantages

1. Smallest in size because of high component density. 
2. Very reliable. 
3. Heat generated is negligible. 
4. No air conditioning required in most cases. 
5. Much faster in computation than previous generations.
6. Hardware failure is negligible and hence minimal maintenance is required.
7. Easily portable because of their small size.
8. Totally general purpose.
9. Minimal labor and cost involved at assembly stage.
10. Cheapest among all generations.

Disadvantage

1. Highly sophisticated technology required for the manufacture of LSI chips.

Fifth generation (yet to come)

Scientists are now at work to bring a machine with genuine I.Q., the ability to reason logically, and with real knowledge of the world.

The main features are:

1. In structure it will be parallel and will be able do multiple tasks.
2. In nature it will be knowledge information processing system (KIPS) and not data processing (DIPS).
3. In application it will be an expert.

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Introduction to Computers

The word computer has evolved from the word compute, which means, "calculate." So a computer is normally considered to be a calculating device that can perform arithmetic operations at enormous speed.

More accurately, a computer may be defined as a device that operates upon data and produces information. Data are raw facts and figures and when they are given a meaningful shape by processing, they are called information. A computer does this processing. So we can call a computer a data processor.

Features of computer

Speed: A computer is a very fast device. It can perform in a few seconds the amount of work that a human being can do in the entire year. While talking about the speed of a computer, we do not talk in terms of seconds r millisecond (10^-3) .The unit of speed of a computer is microsecond (10^-6), nanosecond (10^-9) and even the picoseconds (10^-12). A powerful computer is capable of performing about 3 to 4 million simple arithmetic operations per second.

Accuracy: The accuracy of a computer is consistently high and the degree of accuracy of a particular computer depends upon its design. But for a particular computer, each and every calculation is performed with the same accuracy. The errors can occur in a computer, but these are mainly due to human rather than technological weaknesses, that are due to inaccurate data or due to imprecise thinking by the programmer.

Diligence: Unlike human beings, a computer is free from monotony, tiredness, lack of concentration etc., and hence can work for hours together without creating any error and without grumbling. Due to this property, computers obviously score over human beings in doing routine type of jobs, which require great accuracy. If ten million calculations have to be performed, a computer will perform the tenth million calculations with exactly the same accuracy and speed as the first one.

Versatility: Versatility is one of the most wonderful things about the computer. One moment, it is preparing the result of an examination, the next moment it busy preparing bill and in between it may prepared a letter for a friend. All that is required to change its talent is to switch from one program to another.

Power of remembering: As a human being acquires new knowledge, the brain subconsciously selects what it feels to be important and worth retaining in its memory, and relegates unimportant details to the back f the mind or just forgets them. This is not the case with a computer, which can store and recall any amount of information because of its secondary storage capability.

No I.Q.: A computer posses no I.Q. of its own. It has zero intelligence.

No feelings: Computer is devoid of emotions. They have no feelings and no instincts because they are machine.

Uses of Computer

There are numerous areas where computers are used but some fields cannot work without a computer in this century.

1. Weather forecasting: Super computers are used in the meteorological department to forecast the weather conditions in the country and the world. The prevailing weather conditions are fed into the computer as parameters and then it predict about the atmosphere and weather in the coming hours and the bad weather conditions.
2. Census: Census is the task, which requires data collection, storage and evaluation. This job cannot be done manually and if done would generate errors. This job can be easily done with the computer where a computer can store the lists, sort and merge and count the data very easily.
3. Oil exploration: Oil exploration is easily done with the help of super computers. These computers provide fire alarms, danger signals, and temperature parameters to the scientists, These jobs if manually done would definitely lead to mishapes or mistakes.
4. Speech recognition: This task involves the recognition of the voice of various persons. The voice is stored in the computer and they can be converted to written text) Sometimes the text can be converted into voice. This branch of computer is called artificial intelligence and it is extremely useful when a human being is to be substituted by a machine.
5. Banking and commerce: Today banking and commerce is handicapped without computer. ATM cards are used to with draw money, which is inserted, and the reader reads the magnetized strip. Besides MICR is used to read the cheque number from cheques. This reduces human mistakes and simultaneously increases the speed of the job. All the account balances etc. are also stored in computer for future calculations etc.
6. Publishing: Computer are used in the design of newspapers, magazines, newsletters, brochures etc. All publishing work can be easily done with the help of a computer. PageMaker, CorelDraw etc. are softwares which can produce attractive layouts of magazines, cover pages, newspapers etc.
7. Accounting: Accounting is done with the help of various accounting softwares like TALLY etc. This software accepts the data and generates, profit and loss statement, balanced sheets. Etc. very easily, which is otherwise very difficult.
8. Research: In research, various super computer are used which store data and generate various forecast and results.

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