Classification of Computers

  • There are essentially two different types of computer processing technology. Each is made possible by a different kind of circuitry, and each is suitable for different purposes.
  • Computers are broadly classified into three major categories,on the basis of technology used in this computer –

(X) Analog Computers (Y) Digital Computers (Z) Hybrid Computers 

(X) Analog Computers

  • The name analog comes from the word ‘analogous’, meaning similar.
  • They work on/using analog data or signal.
  • Analog signal is a continuous signal whose amplitude can take any value in a continuous range.
  • It can have infinite number of values.
  • They are generally special purpose computer.
  • It is a machine that specializes by measuring in processing.
  • Analog signal
    • It is a continuous signal whose amplitude can take any value in a continuous range.
    • It can have infinite number of values.
  • Analog computers deal with quantities that are continuously variable.
  • They give only approximate results.
  • These types of computer provide an analog or simulation of the object or system it represents.
  • It is especially useful for solving problems that involve relationships between variable quantities in systems that change with time.
  • The analog compute may express changing relationships in output in the form of graphs.
  • It is able to create such pictures because it responds to changes in electrical voltages that match changes in variable quantities.
  • It is especially useful for solving problems that involve relationships between variable quantities in systems that change with time.

(Y) Digital Computers

  • It is a machine that specializes in counting.
  • A digital computer is an electronic device that receives data, performs arithmetic and
     logical operations and produces results according to a predetermined program.
  • It receives data through an input device (usually keyboard) and displays the results to some output device (usually monitor).
  • All data processing in a digital computer is done by a central processing unit, also known as processor.
  • A working memory is used to store data and instructions in a digital computer.
  • It operates by counting values that are discrete, or separate and distinct, unlike the continuous quantities that can be measured by the analog computer.
  • Digital signal is a discrete time signal that has a discrete number of levels.
  • It can only assume one of the two discrete values 0 or 1.
  • While analog technology uses continuous signals, digital technology encodes the information into discrete signal states.
  • Digital Computers are used for both business data processing and accuracy.
  • The basic operation performed by a digital computer is addition.
  • It can store the sums of addition problems as they accumulate, and can complete a single calculation in a fraction of a nanosecond.
  • The digital computer is capable of storing data as long as needed, performing logical operations, editing input data, and printing out the results of its processing at high speed.
  • Advantages of digital systems include flexible processing, easy to design, accuracy and precision, simple operation, easy data storage, less prone to noises etc.
  • Digital computers are electronic devices which operate on two valued logic (On and OFF).
  • The ability of a transistor to act as a switch is the key to designing digital computers.
  • The digital circuits used in digital computers are bi-stable, one state each corresponding to ON and OFF values. The two valued Boolean logic (using two distinct symbols 0 and 1) serves as an appropriate representation of states of digital circuits. Every instruction and data item therefore needs to be represented only by using two symbols 0 and 1.
  • A digital machine is capable of executing 400-500 distinct instructions and a unique binary code is required to specify every instruction, the machine instructions are specified using multiple bits (binary digits). Similarly, the data items also need to be specified using 0 and 1 only. Numbers, alphabets and other characters can be represented by using some binary code system.
  • Data Processing Capacity :
    • The term “capacity of computer” refers to the volume of work or the data processing capacity a computer can perform.
    • The performance of a computer is judged by the : –
      • Amount of data that can be stored in memory.
      • Speed of internal operation of the computer.
      • Number and type of peripheral devices
      • Amount and type of software available for use with the computer
    • The capacity of early generation computers were determined by their physical size- the large the size, the greater the volume.
  • It is a digital computer system under the control of a stored program that uses a microprocessor, a programmable read-only memory (ROM), and a random-access memory (RAM).
  • The ROM defines the instructions to be executed by the computer while RAM is the functional equivalent of computer memory.

Classification of Digital Computers

  • As we know that computers are available in different sizes, shapes, and weights. Due to these different sizes and shapes, they perform different sort of jobs from one another.They can be classified in different ways.
  • All the computers are designed by qualified computer architects who design these machines as per different requirements.
  • Computers are classified into various categories in different ways –

(A) On the basis of its development/evolution, they are of following types – 

(a) First Generation Computer (b) Second Generation Computer (c) Third Generation Computer (d) Fourth Generation Computer (e) Fifth Generation Computer 

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(B) On the basis of purpose/use of computers in various applications, computers are of         following types –

(a) General Purpose Computer (b) Special Purpose/Dedicated Computer

(a) General Purpose Computer

    • When a computer is designed for doing/able to perform a variety of computing tasks, is called general purpose computer.
    • They are normally able to accept different applications.
    • Most computers in use today are General-Purpose computers.
    • A general purpose computer is able to perform a wide variety of operations because it can store and execute different programs in its internal storage.
    • Simply by using a general purpose computer and different software, various tasks can be accomplished, including writing and editing (word processing), manipulating facts in a data base, tracking manufacturing inventory, making scientific calculations, or even controlling organization’s security system, electricity consumption, some business works etc.
    • Examples – Most of the digital computers are of this nature i.e. All mainframes, servers, laptop and desktop computers, as well as smartphones and tablets are general-purpose devices.
    • ENIAC, was the first general-purpose computer.     

(b) Special Purpose Computer

    • A special-purpose computer is designed to be task specific and most of the times their job is to solve one particular problem.
    • They are also known as dedicated computers, because they are dedicated to perform a single/specific task over and over again.
    • Special-purpose computers are generally designed to solve problems repeatedly in accordance with previously prepared programs while periodic or continuous changes occur in the input data. 
    • The most common examples of special purpose computers are pipeline processors architectures for graphics, with at least 3 companies (AMD, Nvidia, Intel) producing graphics processors that they call GPUs specifically for computer graphics.
    • Examples – Most of the analog and some digital computers are of this nature.
    • Such a computer system would be useful in playing graphic intensive Video Games, traffic lights control system, navigational system in an aircraft, weather forecasting, satellite launch/tracking, oil exploration, in automotive industries, keeping time in a digital watch, or Robot helicopter etc.
    • As these computers have to perform only one task, therefore, they are fast in processing. 
    • These computer’s lack versatility and hence It cannot be used to perform other operations.      

(C) Computers are available in different sizes, shapes, and weights. Due to these different sizes and shapes, they perform different sort of jobs from one another. On the basis of different sizes, shapes, and weights computers are of following types –

(a) Micro Computer (b) Mini Computer (c) Mainframe Computer (d) Super Computer

(a) Micro Computer

      • They are small size computers.
      • Today microcomputers are also popularly called as Personal Computers and are more accurately called as IBM PCs and Apple Macintosh.
      • Intel’s founder, Robert Noyce, chartered Ted Hoff’s Applications Research Department in 1969 to find new applications for silicon technology -the microcomputer was the result.
      • Since microcomputers originally designed for personal use they are also refereed to as personal computer or PCs. Due to the advancement in hardware technology, powerful PCs have been developed since the 1980s.
      • The essential characteristics of these microcomputers are : –
        • Small size and low cost.
        • Single user computer.
        • Easy to use.
        • Comparatively low computing power but sufficient.
        • Commonly used for personal application.
      • The micro computers contain single processor/microprocessors that literally contain a complete processor on a single chip.
      • Microcomputers memories are generally made of semiconductors fabricated on silicon‟s chips.
      • It is a digital computer system under the control of a stored program that uses a microprocessor, a programmable read-only memory (ROM), and a random-access memory (RAM).
      • The ROM defines the instructions to be executed by the computer while RAM is the functional equivalent of computer memory.
      • These are small, relatively inexpensive computers designed for personal use in home, offices and small business.
Examples of Micro/Personal Computers : 

(i) Workstations :

        • A workstation is a high-performance micro computers which are used for scientific and technical tasks such as computer graphics, scientific simulation, computer-aided-design (CAD), image processing, engineering calculations etc.
        • It is generally used in such applications which require a moderate amount of computing power. Hence, the configuration of workstation used to be high.
        • UNIX and Windows NT are the most common Operating System for workstations.
        • Workstations are generally single user system however they can be connected together to form a LAN.
        • In the context of networking, workstations are sometime referred to as any computer/terminal attached to a LAN.
        • In networked workstation, system administrator tracks and controls the activities of the user.
        • The term workstation is also used for high capacity mainframe computer terminal or a PC connected to a network and working in client server mode.
        • A workstations has superior processing and storage capabilities than a normal PC , especially with respect to providing multitasking capability.

(ii) Personal Computer (PC) :

        • A personal computer (PC) is a general-purpose computer, used for day to day activities in different areas including education, business, administration and health.
        • Due to its size and capabilities, PC is useful for the users.
        • A PC can be operated directly and may be used for computational, word processing, and data storage purpose.
        • Depending on the size and processing capacity, PCs are of many types such as, a desktop computer, a laptop, tablet PC, a handheld PC /palmtop.
        • Personal computers can be connected to the computer network by wired or wireless media.
        • PCs are being used from a school going children to a business professional for different purposes. A non-professional user may use a PC to listen songs, watching movies, creating some documentation, email etc. A professional user may use a PC for different business process such as documentation, running business program, creating databases, internet, and emailing, teleconferencing etc. Thus, the scope of a personal computer varies a lot depending on the type of its users.
        • The configuration of a PC matters a lot in terms of its processing quality and cost.
        • The most common PCs are – 

    (a) Desktop Computers :

          • Desktop computer is popularly known as personal computer (PC).
          • As the name suggest, it is generally small in size and fitted on the top of a desk which can be used at a fixed location.
          • Most of modern desktop computer has separate monitor screens and keyboards.
          • Generally in majority of the PCs, Microsoft Windows, LINUX and Mac OS x are used as operating system.
          • Desktop computers are available in many different forms from large vertical tower cases to small form factor models.
          • Advantages of desktop computer are that it may be used for day to day computational and internet communication activities of office, school etc.
          • A PC provides more space for heat to escape. Also power consumption of a PC is not very high.
          • There are many brands of PCs are available in Indian market and abroad including HP, HCL, Wipro, Compaq etc.
          • A PC also can be assembled as per specific requirements, instead of a particular brand.

    (b) Laptop Computers :

          • Laptop is also a personal computer but intended of using it at a single place.
          • It is small size, portable and can be used anywhere.
          • Portability is one of the main advantage of a Laptop over a table PC.
          • Another advantage of a Laptops is that it contain batteries which are used for power supply. It make a laptop usable even if power is not available.
          • In a laptop almost all the components are attached as a single unit. Although some devices like mouse, can be attached externally through ports.
          • The basic components of laptop are similar in function to the desktop computers.
          • Most of modern desktop computer has separate screens and keyboards.
          • Generally in majority of the PCs, Microsoft Windows, LINUX and Mac OS x are used as operating system.
          • Laptops are much more power efficient than desktops.
          • The major disadvantage of Laptop is that its upgradeability is limited as compared to desktops.
          • There are many brands of Laptop are available in Indian market and abroad including HP, HCL, Wipro, Compaq, Dell, Lenovo, Toshiba, Sony etc.

    (c) Notebook Computers :

          • Netbooks are special type of Laptop which is very light and small.
          • Due to its size and weight it is very portable and one may carry it very easily.
          • Dissimilar to Laptop , it does not require a separate carry bag for it.
          • Netbook are suitable for general purpose computing works and for accessing the Internet.
          • They also use less powerful hardware than most laptops.
          • Due to limited processing capabilities Netbooks are less expensive than laptops.
          • Due to its size and portability Netbooks are becoming very popular for education and business works.
          • Works related to word processing, presentation, internet access, multimedia etc can be easily carried out on a Netbook.
          • Generally in Netbooks, Windows, Linux, and Android operating system are used along with others.
          • There are many brands of Netbook available in Indian market and abroad including Acer, HP, Dell, HCL , Apple, Sony etc.

    (d) Tablet PC :

          • A tablet PC is similar to a personal computer.
          • It is a portable device which has a touch screen for inputting of the data.
          • A tablet computer can connect to the internet and local computer network through wireless.
          • In general terms, tablet PC refers to a slate shaped mobile computer device, equipped with global positioning system (GPS) System , and a touch screen to operate the computer.
          • It is generally equipped with office suits such as word, excel etc, web browsers, computer games and other similar applications, that generally can be run on a PC.
          • Tablet PC can also use handwriting recognition and virtual keyboards for input of data.
          • In, tablet PCs Microsoft windows, Linux and Apple operating system are used.
          • There are many brands of Tablet PC available in Indian market and abroad including Acer, Lenovo , Panasonic, and Toshiba etc.

    (e) Smartphones :

                      

    (f) Personal Digital Assistance :

                        

    (b) Mini Computer

        • They are near to medium size computers.
        • Medium-size Computers :
          • It provides faster operating speeds and larger storage capabilities than small computer systems.
          • These Computers can support a large number of high-speed input-output devices, and several disk drives can be used to provide online access processing.
          • The possibility of increasing the data processing capability of a computer by adding devices, such additional memory, and other peripheral devices, is called expandability.
          • Although the minicomputer is not as powerful as the medium or large-size computer, it is quite close.
        • Minicomputer systems (or also called small mainframe computers) provide faster operating speeds and larger storage capacities than microcomputers systems.
        • These Computers can support a large number of high-speed input/output devices.
        • Several desk drives can be used to provide online access to large data files as required for direct – access processing.
        • Operating system developed for minicomputer systems generally support both multi programming and virtual storage i.e. many programs can be run concurrently.
        • This type of computer system is very flexible and can be improvised to meet the needs of users. 
        • Several desk drives can be used to provide online access to large data files as required for direct – access processing.
        • The minicomputer is not as powerful as the medium or large-size computer, rather it is quite close.

    (c) Mainframe Computer

        • They are near to large size computers.
        • Large Size Computers : 
          • These Computers are the ultimate in flexibility and speed.
          • These usually contain full control systems with minimal operator intervention.
          • Large computer systems range from single-processing configurations to nationwide computer based networks involving general large computers.
          • Large computers have internal operating speeds measured in terms of nanoseconds, as a compared to smaller computers where speed in terms of microseconds.
        • Mainframe computers are huge, multi-user systems designed to process millions of instructions per second and capable of accessing billions of data.
        • They can handle gigantic processing jobs in large corporations or government agencies.
        • This computer is commonly used in big hospitals, air line reservations companies and many other huge companies prefer mainframe because of its capability of retrieving data on huge basis.
        • Mainframe allows its user to maintain large information storage at a centralized location and be able to access and process this data from different computers located at different locations.
        • Mainframe computers are normally too expensive and out of reach from a salaried person who wants this computer for his home.
        • Mainframe is the second largest in capability and size of computer family.

    (d) Super Computer

        • They are near to largest size computer.
        • The most expensive in price, biggest and fastest machines today are the supercomputers that are used when billions or even trillions of calculations are needed.
        • Supercomputers are ultra fast computers designed to process huge amounts of scientific data then display the underlying patterns that have been discovered.
        • These machines are essential for applications ranging from nuclear weapon to accurate weather forecasting.
        • Super Computers are used for highly calculation-intensive tasks such as molecular modeling, climate research, weather forecasting, quantum physics, physical simulations etc.
        • Supercomputers are machines that have speed in the 100-million-instructions-per-second range.
        • Governments specially use this type of computer for their different calculations and heavy duty.
        • Different industries also use this huge computer for designing their products.
        • It is also used for animation purpose.
        • The PARAM supercomputer is one of the supercomputer developed by India‟s Center for Development of Advanced Computing(C-DAC) and promises processing speeds of up to 1 trillions instructions per second.
        • Since October 2010, the Tianhe-1A supercomputer is considered as the fastest supercomputer in the world which is located in China.
        • Some of the examples of Supercomputer are: IBM Blue Gene/L, IBM Roadrunner, Cray Jaguar etc.

                 

    (Z) Hybrid Computers 

    • A computer that combines the best features of both the types of computer i.e. analog and digital computer.
    • This is a special-purpose machine called a hybrid computer which combines the measuring capabilities of the analog computer and the logical and control capabilities of the digital computer.
    • It offers an efficient and economical method of working out special types of problems in science and various areas of engineering.
    • Some Hybrid machines contain special equipment to convert analog voltages into digital voltages, and vice-versa.

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