What is Computer Architecture?Components of Computer.

Computer architecture deals with the functional behaviour of a computer system as viewed by a programmer. It can also be described as the logical structure of the system unit that housed electronic components. The Computer architecture Forms the backbone for building successful computer systems.

What is computer architecture?

Components of Computer

A computer consists of the following main components.

  • Input/Output Unit
  • Central Processing Unit
  • Memory Unit

Input Unit

The Computer accepts coded information through input unit by the user. It is a device that is used to give request information to the computer. E.g. keyboard, mouse, etc. An input unit performs the following functions.

  1. It accepts the instructions and data from the user.
  2. It converts these instructions and data in computer in acceptable format.
  3. It supplies the converted instruction and data to the computer system for further processing.

Output Unit

This Unit sends the Processed result to the user. It is mainly used to display the desired result to the user as per input instruction. E.g. video monitor, printer and plotter, etc.

The following functions are performed by an output unit.

  1. It accepts the result produced by the computer which are in coded form and hence cannot be easily understood by us.
  2. It converts these coded results to human acceptable form.
  3. It supplies the converted results to the user.

Central Processing Unit (CPU)

It consists of a set of registers, arithmetic logic unit and control unit, which together interpret and execute instructions in assembly language. 

The primary functions of the CPU are as follows.

  1. The CPU transfers instructions and input data from main memory to registers, i.e. internal memory.
  2. The CPU executes the instructions in the stored sequence.
  3. When necessary, CPU transfer output data from registers to main memory.

Central Processing Unit is often called the brain of the computer. The CPU is fabricated as a single Integrated Circuit (IC) and is also known as microprocessor. A CPU controls all the internal and external devices and performs arithmetic and logic operations.

The CPU consists of following main sub-systems.

Arithmetic Logic Unit

ALU contains the electronic circuitry that executes all arithmetic and logical operations on the available data.

ALU uses registers to hold the data that is being processed.

Most ALUs can perform the following operations.

  1. Logical operations (AND, NOT, OR, XOR).
  2. Arithmetic Operations (addition, subtraction, multiplication and division).
  3. Bit-shifting operations (shifting or rotating a word by a specified number of bit to the left or right with or without sign extension).
  4. Comparison operations (=,<, <=, >, >=)

Registers – These are special purpose and high speed temporary memory units. Registers are not referenced by their address, but are directly accessed and manipulated by the CPU during execution. Registers store data, instruction, address and intermediate results of processing. The number and size of registers vary from processor to processor.

Control Unit

CU coordinates with the input and output devices of a computer. It directs the computer to carry out stored program instructions by communication with the ALU and the registers. It organises the processing of data and instructions.

The basic function of control unit is to fetch the instruction stored in the main memory, identify the operations and the devices involved in it and accordingly generate control signals.

Microprocessor –  The microprocessor is the controlling element in a computer system and is sometimes referred to as the chip. Microprocessor is the main hardware that drives the computer. It is a large Printed Circuit Board (PCB), which is used in all electronic systems such as computer, calculator, digital system, etc. The speed of computer, calculator, digital system, etc. The speed of the CPU depends upon the type of microprocessor used.

  • Intel 4004 was the first microprocessor made by Intel in 1971 by scientist Ted Hoff and engineer Frederico Faggin.
  • Some of the popular microprocessor are intel core i7, intel, Dual core, Pentium IV, etc.

Memory Unit

This unit is responsible to store programs or data on a temporary or permanent basis. It has primary memory (main memory) and secondary memory (auxiliary memory). The input data which is to be processed is brought into main memory before processing.

The needed instruction for processing and any kind of intermediate results are also stored in primary memory. Together with these, the final output is also stored in primary memory before transferring it to the output unit. Another kind of memory is referred to as secondary memory of a computer system. This unit is used to permanently store data, programs and output. This unit does not deal directly with CPU.


The main circuit board contained in any computer is called a motherboard. It is also known as the main board or logic board or system board or planar board. The biggest pieces of silicon housed in the system unit of a computer is the motherboard.

All the other electronic devices and circuits of computer systems are attached to this board like, CPU, ROM, RAM, expansion slots, PCI slots and USB ports. It also included controllers for devices like the hard drive, DVD drive, keyboard and mouse. In other words, motherboard makes everything in a computer work together.

Interconnection of Units

CPU send data, instructions and information to the components inside the computer as well as to the peripheral devices attached to it.

In other words, A bus is a set of wires used for interconnection, where each wire can carry one bit of dat. In other words, but is a set of electronic signal pathways that allows information and signals to travel between components inside or outside of a computer.

A computer bus can be divided into two types.

  • Internal Bus – The Internal bus connects components inside the motherboard, CPU and system memory. If is also called the system bus.

Internal bus includes following buses.

  1. The address of I/O device or memory is carried by the address bus. The data to be transferred is carried by the data bus.
  2. The address of I/O device or memory is carried by the address bus. The data to be transferred is carried by the data bus.
  3. External Bus The external bus connects the different external devices, peripherals, expansion slots, I/O ports and drive connections to the rest of the computer. It is also referred to as the expansion bus.
  • UPS – (Uninterruptible Power Supply), is an electrical apparatus that provides emergency power to a load when the input power source or mains power fails.
  • Buffer – is a temporary storage where registers hold the data for further execution.
  • Accumulator is a register in the CPU in which intermediate arithmetic and logic results are stored.
  • The performance of the computer is affected by the size of registers, size of RAM, speed of system clock and size of cache memory.
  • The speed of a processor is measured in millions of cycles per second or megahertz (MHz).

Instruction Cycle

The instruction cycle represents the sequence of events that takes place as an instruction is read from memory and executed.

A simple instruction cycle consists of the following steps.

  1. Fetching the instruction from memory.
  2. Decoding the instruction for operation.
  3. Executing the instruction.
  4. Storing in memory.

In the above steps, step 1 and 2 instructions are same and known as fetch cycle and step 3 and 4 instructions are different and known as execute cycle.

Instructions Format

Computer understands instructions only in terms of 0’ and 1’s, which is called the machine language. A computer program is a set of instructions that describe the steps to be performed for carrying out a computational task. The processor must have two inputs, instructions and data.

The Instructions tell the processor what actions are needed to be performed on the data. An instruction is further divided into two parts, operation (op-code) and operand. The op-code represents action that the processor must execute and the operand defines the parameters of the action and depends on the operation.

  • Machine cycle is defined by the time that takes to fetch two operands from registers and perform the ALU  operation and stored the result in a register.
  • Pipelining improves execution speed by putting the execution steps of several instructions in parallel.
  • Sockets are the connecting points of chip on the motherboard.
  • Load instruction is used for loading data into CPU accumulator register from memory.

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Brief Introduction of Computer- History, Features, Classification and Application of the Computer.

A computer is an electronic machine that accepts data from the user, process the data by performing calculation and operation on it and generates the desired output as a result. The term computer is derived from the latin word ‘computare’ which means ‘to computer’.

Generally, the computer is the combination of Hardware  and Software which converts data into information. Computer operates on set of instructions only, they cannot think as a human being. Computer has an ability to store and execute a set of instructions called program which makes it extremely distinguishable and versatile than calculators. Computer makes people’s lives easier and more comfortable.

Functioning of a Computer

Computer performs four functions which are as follows

  1. Input:- Information or data that is entered into a computer is called input. It sends data and instructions to the Central Processing Unit (CPU).
  2. Processing:- It is the sequence of actions taken on data to convert it into information which is meaningful to the user. It can calculations, comparisons or decisions taken by the computer.
  3. Output:- It makes processed data available to the user. It is mainly used to display the desired result to the user as per input instructions.
  4. Storage:- It stores data and programs permanently. It is used to store information during the time of program executions and possible to get any type of information from it.

Features of Computer

The key features of computer are as follows.

  1. Speed:- The Computer can process data very fast at the rate of millions of instructions per second.
  2. Accuracy:- Computers provide a high degree of accuracy. They respond to the user as per the input instructions.
  3. Storage Capacity:- Computers are capable to store huge amount of data which depends on the capacity of the hard disk.
  4. Versatility:- Computers can do different types of work simultaneously. They can perform multiple tasks at the same time.
  5. Automatic:- Once the instruction to do any work is given to the computer, the computer does its work automatically by itself.
  6. Diligence:- Unlike human beings, a computer is free from monotony, tiredness, lack of concentration, etc and can work for hours without creating any errors.
  7. Secrecy:-  Leakage of information is reduced by creating a login system with password protection.
  8. Reliability:- Computer are more reliable than human beings. Computers always produces exact results. The possibility of errors occur only if the input is wrong, i.e. the computers never make mistakes of their own accord.
  9. Plug and Play:- 

History Of Computer

Computer is not the creation of one day, rather it took a long period for the development of modern computers. History of computer is described in this table.

Abacus – 1602ChinaFirst mechanical calculating device.A horizontal rod represents the one, tens, hundreds, etc.Used for addition and subtraction operations.Calculation of square roots can also be performed.
Napier’s  bones 1617John NapierThree dimensional structure.Holding numbers from 0 to 9 only.Represents graphical structure of calculating result.Perform multiplication on numbers.Technology used for calculation called Robdologia.
Pascaline – 1642Blaise PascalFirst Mechanical adding machine.It was structured like rectangular box, with eight disc (represent number of units).Perform addition and subtraction of two numbers.Mainly designed with regard to the pressure of liquid.
Jacquard’s Loom 1801Joseph Marie JacquardMainly weaved a silk based pattern.Used punched card for the sequence of operation.Simplified the process of Textiles.
Analytical Engine 1837Charles Babbage (Father of computer)First general-purpose computer.Stored program in the form of ‘pegs’ also called barrels.It was a decimal machine used sign and magnitude for representation of a number.
Tabulation Machine 1880Herman HollerithIt used punched cards with round holes.It was the first electromechanical machine designed to process the data for census in 1890.Read one card at a time.
Mark-1 1944Howard AikenConsists of interlocking panels of small glass, counters, switches and control circuits.Data can be entered manually.Mainly used in the war effort during world war-II.Magnetic drums are used for storage.
ENIAC 1946JP Eckert and JW MauchlyIt is a combination of twenty accumulators.First electronic digital computer.Used for weather prediction, atomic energy calculation and other scientific uses.
EDSAC 1949John Von Morris WilcusIt was the first computer which provide storage capacity.First computer program was run on machine.Capable of storing instructions and data in memory.Used mercury delay lines for memory, vacuum tubes for logic.
UNIVAC 1951Eckert John MauchlyFirst general-purpose electronic computer with large amount of input and output.Used magnetic tapes as input and output.
IBM-650 Computer 1954IBM CompanyProvide input/output units converting alphabetical and special characters to two-digit decimal code.Payroll processing.Oil refinery design.Market research analysis.

Generation of Computer

A generation refers to the state of improvement in the development of system. Computers are built of electromagnetically, before generation. Each generation of computer is characterized by a major technological development that fundamentally changed the way computers operate.

GenerationSwitching DeviceStorage DeviceSpeedOperating SystemLanguageCharacteristicsApplication
First (1940-56)Vacuum TubesMagnetic drums333 microsecondBatch operatingMachine languageFastestHeatnot-portableUsed for scientific purpose
Second (1956-63)TransistorsMagnetic core technology10 microsecondTime sharing systemAssembly languageMore reliableHardware failureLess amount heat
Used for commercial purpose
Third (1964-71)ICPrimary storage medium100 nano secondReal time systemHigh level languageConsume less powerHigh sophisticatedDatabase m system
Fourth (1971-Pres.LSISemiconductor memory300 nano secondTime sharing gui interfacePascal, ada, cobolMore reliableBetter communicationDistributed system
Fifth (Present)SLSIOptical disk—–Processing system
Parallel processingEnable mega chips.Robotics 

Classification of Computer

Computers are mainly classifieds as three types as follows.

Types of Computer -Based on Size

On the basis of size, computers are categorized as follows.

Microcomputer – Microcomputers are the least powerful, yet the most widely used and fastest growing type of computers and are also called portable computers. Microcomputer consists of three basic categories of physical equipment, i.e. system unit, input/output unit and memory unit.

Some types of microcomputer are as follows.

  • Desktop Computer or Personal Computer:- These are small, relatively inexpensive computers. There are based on the microprocessor technology (IC). In 1958, Jack Kilby and Robert Noyse invented the first IC.
  • Laptop:- These computers are also known as ultrabook or notebook. These are portable, lightweight and fit into most briefcases. They included rechargeable battery, so these can work anywhere.
  • Handheld Computer:- These are the smallest and are designed to fit the palm. So, these are also known as palmtop. They are practical for certain functions such as phone books and calendars. They use the pen for input instead of keyboard.
  • Tablet Computer:- They have key features of the notebook computer but these can accept input from a pen instead of a keyboard or mouse.
  • Personal Digital Assistant:- It is also known as a handled PC, or personal data assistant, is a mobile device that functions as a personal information manager.

Minicomputer – Minicomputer are smallest in size, fatest, cost lower than mainframe computers. Initially, the minicomputer was designed to carry out some specific tasks, like engineering and computer aided design calculations. But now, they are being used as central computer which is known as server. Minicomputer are IBM-17, DEC PDP-11, HP-9000, etc.

Mainframe Computer – Mainframe computers are those having large internal memory storage and comprehensive range of software. Mainframe computer serves as a backbone for the entire business world. It is considered as the heart of a network of computers or terminals that allows a large number of people to work at the same time. Mainframe computers are IBM-370, IBM-S/390, UNIVAC – 1110, etc.

Supercomputer – Supercomputers are the fastest and most expensive machines. They have high processing speed compared to other computers. The speed of supercomputers are measured in FLOPS(Floating Point Operations Per Second). Supercomputers are used for highly calculation intensive tasks, such as weather forecasting, nuclear research, military agencies and scientific research laboratories. Supercomputer are most powerful, large in size and memory, compared to all other computers.

Computer Types Based on Work

On the basis of work, computers are categories as follows.

Analog Computer – Analog computers are the job-oriented computers. They carry out arithmetic and logical operations by manipulating and processing of data. E.g. speedometers, seismographs, etc. Analog Computer can perform several mathematical operations simultaneously. It uses continuous variable for mathematical operations and utilize mechanical or electrical energy.

Digital Computer – Digital Computer work by calculating the binary digits.  A digital computer, not only performs mathematical calculations, but also combines the bytes to produce desired graphis, sounds. E.g. desktop (PC).

Hybrid Computer – Hybrid computers are the combination of analog and digital computers. Machines used in hospitals like ECG and DIALYSIS are the commonly used hybrid computers.

Computer Types Based on Purpose

On the basis of purpose, computers are categorized as follows.

General Purpose Computer – General purpose computers are those computers, which are used to solve a variety of problems by changing the program or instructions. E.g. to make small database, calculation, accounting, etc.

Special Purpose Computer –  special purpose computers are those computers which are used to solve a single and dedicated type  of problems. E.g. automatic aircraft landing multimedia computer, etc.

Application Of computer

Now a days computers have been employed in almost all the aspects of professional and personal life. Some of the areas where computers are being used are as follows.

  1. Education:- Computer have proved to  be excellent teachers. Educational institutes are using computers in many ways like tele-education, virtual classroom, online classes, etc.
  2. Science and Engineering:- Scientists have been long users of it. A new adventure among scientists is the idea of collaboratory, an internet based collaborative laboratory, in which researchers all over the world can work easily together even at a distance.
  3. Industry:- Computers are used here to control manufacturing system and continuous running of the machinery. Parameters like temperature, pressure, volume are monitored and controlled by computers. Robotics developed with the help of computers play a very crucial role here.
  4. Recreation:- Our entertainment and pleasure time have also been affected by computerisation.
  5. Administration:- Various departments of the government use computer for their planning, control and law enforcement activities.
  6. Health:- Computer plays a very crucial role in this area. Activities like scanning, X-ray, tele-medicine, patient monitoring, patient records, diagnosis, etc. are performed with the help of computers.
  7. Multimedia:- It is the field concerned with the computer controlled integration of text, graphics, drawings, animation, audio and any other media where each type of information can be represented, stored transmitted and processed digitally.
  8. Banks:- Computers can be used in the banks to keep the records of customer’s accounts.
  9. Military Personnel:- They also make use of computers for their crucial tasks like determining the weather, computing the trajectories of missiles etc.
  10. Business:- Using a wide range of business software a company’s marketing division can produce sales forecast and devise new strategies.
  11. Commerce:- It is the activity of buying and selling of goods and services, especially on a large scale.
  12. Publication:- Computers have made publication process an easy one. Without computers, the different parts of a publication-text, illustrations and graphics-must be created individually, then cut out and pasted down to form a page layout.

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