What is Computer?

कम्प्युटर के हो

कम्प्युटर एउटा गणितिय र तार्किक भाषामा बुदागत लेखिएका अदेशहरू स्वचालित तरिकाले अबलम्बन गर्ने यन्त्र हो। कम्प्युटर ले आफनै यान्त्रिक भाषा मात्र बुज्दछ । हामिले दिने सबै अदेशहरू कम्प्युटरले पढ्न सकने भाषामा अनुवाद गर्ने कार्यभाषा (program) ले मानब भाषा र कम्प्युटर बीचमा अनुबादकको काम गर्छ । त्यस्तो सम्यन्त्रलाई interpreter भनिन्छ । कम्प्युटर धेरै प्रकारका हुन्छन् . जसमा विभिन्न द्रिस्तिकोण बाट बर्गिकरण गरिएको छ .


 

1. GENERATIONS OF COMPUTERS:

The tem generation indicates the type of technology used in the computer construction. As new technology was emerging, it was being used in the making of computer. The new technology improved the speed, accuracy and storage capacity of the computers. Different technologies have been used for computers in different times.

Therefore, computers can be divided into five generations depending upon the technologies used. These are:

First Generation (1942 – 1955)

Second Generation (1955 – 1964)

Third Generation (1964 – 1975)

Fourth Generation (Since 1975)

Fifth Generation (Since 1980)

1. First Generation Computers (1942 – 1955):

The vacuum tube technology was used in first-generation computers. Mark-1m, ENIAC, EDSAC, EDVAC, UNIVAC-1 etc. machines belong to the first generation of computers. The machine language only was used in first-generation computers.

Principle:-

The vacuum tubes consisted of filaments inside it which on heating emit electrons. These electrons were responsible for the amplification and deamplification of electrical signals.

Input:-

Punched cards

Output:-

Print-outs

Advantages:

• These computers were the fastest of their time.
• They were programmed using machine language.
• The electronic digital computers were introduced due to the vacuum tube technology.    

Disadvantages:

• Very large in size
• Not reliable
• Consumed large amount of energy
• Constant maintenance required
• More heat generated and air-conditioning was required
• More costly
• Very slow in speed (data processing)
• It was difficult to programmed, because they used only machine language
• Non-portable
• Limited commercial use

2. Second Generation Computers (1955 – 1964):

The transistor technology was used in second-generation computers. The electronic component transistor was invented in 1948 at Bell Laboratories. The transistor is smaller in size and more reliable than vacuum tube. Therefore, the transistor technology was used in computer in place of vacuum tube technology. The programming assembly language was also introduced in second-generation of computers.

The transistors consisted of BASE, COLLECTOR and EMITTER. Their functions include:-

BASE: input gate for the transistor.

COLLECTOR: collect the amplified signals

EMITTER: output gate for emitting the amplified signals to the external environment.

Advantages:

• Low in cost
• Smaller in size
• Fast in speed
• Less heat generated more reliable and accurate in calculations
• Consume low power etc.
• Used for commercial purposes
• Portable
• Assembly language was introduced. This language is easy to write program than machine language

Disadvantages:

• Air-conditioning required
• Commercial production was difficult and these were very costly
• Constant (or frequent) maintenance required
• Only used for special purposes

3. Third Generation Computers (1964 – 1975):

The IC (Integrated Circuits) technology was used in third-generation computers. In a small IC chip (5 mm square size) a circuit is designed having large number of electronic components like transistors, capacitors, diodes, resistors etc. Initially, an IC contained only about ten to twenty components. Thus the IC technology was named as Small Scale Integration (SSI). The third-generation was based on IC technology and the computers were designed using this technology.

Advantages:

• Smaller in size
• Production cost was low
• Very fast in computational power
• More reliable
• Low power consumption
• Maintenance cost was low because failure rate of hardware was very low
• Magnetic disk, used for external storage
• More storage capacity
• Easily portable
• Easy to operate
• Upgraded easily
• Widely used for various commercial applications all over the world
• Lower heat generated
• High-level languages were commonly used
• Many input/output devices were introduced such as mouse and keyboard etc.

Disadvantages:

• Air-conditioning required
• Highly sophisticated technology required for the manufacturer chips

4. Fourth Generation Computers (1975 onwards):

The microchip technology was introduced in this generation of computers. With the advancement in IC technology, LSI (Large Scale Integration) chips were developed. It was possible to integrate over 30,000 or more components on to single LSI chip. After LSI, the VLSI (Very Large Scale Integration) was developed and the development of microprocessor possible. It is expected that more than one million components will be integrated on a single chip of VLSI. Using VLSI technology, the entire CPU is designed on a single silicon chip. The use of microprocessor as CPU introduced another class of computers called the microcomputers. Thus fourth-generation may be called Microcomputer generation. IBM introduced its personal computer for use in 1981.

Advantages:

• Smaller in size
• Production cost is very low
• Very reliable
• Hardware failure is negligible
• Easily portable because of their small size
• Totally general purpose
• Air conditioning is not compulsory
• Very high processing speed
• Very large internal and external storage capacity
• Used advanced input & output devices such as optical readers, laser printers, CD-ROM/DVD-ROM drives etc.

Disadvantages:

Highly sophisticated technology required for the manufacturer of microprocessor chips

5. Fifth Generation Computers (In process):

The main drawback of first to fourth generation computers is that the computers have not their own thinking power. These are totally depending upon the instructions given by the users.

Fifth generation computers are supposed to be the ideal computers, but do not exist. The scientists are working to design such computers that will have the following features.

• Having their own thinking power
• Making decisions themselves
• Having capabilities of learning
• Having capabilities of reasoning
• Having large capacity of internal storage
• Having extra high processing speed 
• Having capabilities of parallel processing

 Technologies used in fifth generation computers:

• ULSIC (Ultra Large Scale Integrated Circuits) technology
• Artificial Intelligence (AI) technology also called the knowledge Processor. The AI means automatic programs that let the machines to think and decide themselves. The programming languages LISP (List Processor) and PROLOG (Programming with Logic) are used for artificial intelligence. The scientists at ICOT in Japan use the PROLOG to develop the Artificial Intelligence software.

Advantages:

• Laptops, Pocket computers and PDA were developed.
• Development of parallel processors
• Development of centralized servers
• Development of optical disc technology
• Invention of internet and its advantages.

2. CLASSIFICATION OF COMPUTERS:

Computers can be classified based on the following criteria:

According to Technology:

• Analog Computers
• Digital Computers
• Hybrid Computers

According to Purpose:

•  General purpose Computers
•  Special Computers

According to size:

• Supercomputers
•  Mainframe Computers
•  Minicomputers
•  Microcomputers, or Personal Computers

Based on operating principles and technology:

Analog computers:

• These computers represent data in the form of continuous electrical signals.
• These are fast and multi-tasked.
• Results displayed by these computers are less accurate.
• Powerful in solving differential equations.
• These computers use OP-AMP (Operational Amplifier).

The features of OP-AMP include:

•  High voltage gain. The voltage gain is defined as the ratio of output voltage to input voltage.
•   Infinite input resistance. The input resistance is defined as the ratio of change in input voltage to the change in input current.
•   Zero output resistance. The output resistance is defined as the nominal resistance measured with nil loads.

$    The basic OP-AMP circuit is represented as:

Wherein, Rin is the input resistance, RF is the feedback resistance A is the amplifier which is used to invert the incoming signals of voltage Vin to Vout.

Digital computers:

$These are called the Digital information processing systems.

$These systems store and process the data in digital form (strings of 0's and 1's)

$They are capable of processing analog signals but the analog signals have to be converted into digital signals using an ADC before feeding into the digital computers.

Hardware components:

$Arithmetic Logical unit (ALU)

$Control unit

$Memory unit

$Input unit

$I/O units

Hybrid computers:

$These are the combination of both Analog and Digital computers encompassing the best features of both the computers.

$Fast, efficient and reliable computer systems.

$The Data is measured and processed in the form of electrical signals and stored with digital components.

$The input is accepted in the form of varying electrical signals and is converted into discrete values for performing operations.

$They are used in hospitals to measure heartbeat and have engineering and scientific applications.

Based on Applications:

General purpose computers:

$   Work in all environments

$   Versatile computers

$   Store number of programs to perform distinct operations

$    More expensive

$   Not efficient and consume large time to generate results

Special purpose computers:

• Work on specific tasks
• Non-versatile
• Speed and memory of these computers depend on the task performed
• More efficient and consumes less time to process results
• Less expensive

Based on size and capability:

Micro-computers:

These are small cheap digital computers for individuals

Hardware components:

Microprocessor, storage unit, I/O channels, power supply, connecting cables.

Software components:

Operating System (OS), Utility software, Device drivers

Available in the forms of:

PC's, Work stations, Notebook computers.

The various components are:

Microprocessors:

This incorporates all functions of the CPU into a single unit. The various units of microprocessor are:

• ALU: performs arithmetic and logical operations.
• Registers: Store data and instructions temporarily needed by the ALU.It includes several types like: Accumulator (ACC), Program Counter (PC), etc. 
• CU: Control unit-Used to manage and control the functions of microprocessors, I/O devices

Memory:

Used to store data and instructions. It is of two types:

 * Primary memory: 

It stores temporarily the data and instructions needed by the microprocessor

 * Secondary memory:

 It stores data permanently. Examples include magnetic tapes, floppy, CD, USB, etc,

Peripheral devices:

 Input devices: 

They are used to transfer data into the computer. Examples: keyboard, mouse, etc,

 Output devices: 

Used to display the results processed by the computer. Examples: Monitor, printer, etc,

System bus:

It is also called the FRONTSIDE BUS, MEMORY BUS, LOCAL or HOST BUS.

It is used to connect microprocessor, memory and peripheral devices into a unit.

    

                                

Address bus: 

Unidirectional bus to identify the peripheral devices and memory.

Data bus: 

Bi-directional bus used to transfer data among the microprocessor, peripheral devices and memory.

Control bus: 

bus used by the microprocessor to send control signals to various devices.

Depending on size, Microcomputers are of three types:

Desktop computers:

They are used in single location, cheap, and have good storage. Examples include: Apple, IBM.

Laptop computers:

Portable computers also called as the notebook computers or mobile computers. They are smaller in size, more expensive and are rechargable.Examples include Apple, Acer, Hewlett Packard (HP)

Hand-held computers:

Also called as Personal Digital Assistants (PDA's), Palmtop or Mobile device. They are smaller in size, have smaller display and input device is generally an electronic stylus. Their storage capacity is small. Examples include Apple Newton, Franklin eBook man.

Mini computers:

These were introduced by Digital Equipment Corporation (DEC) in 1960.

They can process more data and can support more I/O devices

They are less powerful than mainframe computers but more powerful than micro computers. Hence they are called MID-RANGE COMPUTERS.

They cater to the needs of 4-200 users at a time

They are used in business as a centralized computer or as an internet server

They are less expensive than Mainframe computers. Examples include PDP 11, IBM 8000 series, etc,

Mainframe computers:

These are capable of handling millions of records a day.

These are bigger and more expensive than mini-computers

They require a large space and closely monitored humidity and temperature.