Computer Architecture

Discuss the generation of computers?


Development of technologies used to fabricate the processors, memories and I/O units of the computers has been divided into various generations as given below:

•        First generation

•        Second generation

•        Third generation

•        Fourth generation

•        fifth generation

First generation:

1946 to 1955: Computers of this generation used Vacuum Tubes. The computers were built using a stored program concept. Ex: ENIAC, EDSAC, IBM 701.

Computers of this age typically used about ten thousand vacuum tubes. They were bulky in size, had slow operating speed, short lifetime and limited programming facilities.

Characteristics of 1st Generation Computers

  • These computers were designed using vacuum tubes.
  • Programming in these computers was done using machine languages.
  • The main memory of 1st Generation Computers consisted of magnetic tapes and magnetic drums.
  • Paper tapes and Punched cards were used as input/output devices in these computers.
  • These computers were very huge but worked very slowly.
  • Examples of 1st Generation Computers are IBM 650, IBM 701, ENIAC, UNIVAC1, etc.

Second generation:

1955 to 1965: Computers of this generation used the germanium transistors as the active switching electronic device. Ex: IBM 7000, B5000, IBM 1401. Comparatively smaller in size About ten times faster operating speed as compared to first generation vacuum tube based computers. Consumed less power, had fairly good reliability. Availability of large memory was an added advantage.

Characteristics of Second-Generation Computers

  • The Second Generation computers used the technology of Transistors.
  • Machine language and Assembly Languages were used for these computers.
  • Magnetic core and magnetic tape/disk were used for memory storage.
  • The Second Generation Computers were smaller in size, consumed less power and generated less heat.
  • Magnetic tape and punched cards were used as input/output devices.
  • Some of the examples are PDP-8, IBM1400 series, IBM 7090 and 7094, UNIVAC 1107, CDC 3600, etc.

Third generation:

1965 to 1975: The computers of this generation used the Integrated Circuits as the active electronic components. Ex: IBM system 360, PDP minicomputer etc. They were still smaller in size. They had powerful CPUs with the capacity of executing 1 million instructions per second (MIPS). Used to consume very less power consumption.

Characteristics of Third-Generation Computers

  • These computers were built using Integrated Circuits (ICs).
  • High-level programming languages were used for programming on these computers.
  • Large magnetic core and magnetic tape/disk were used for memory storage.
  • Magnetic tape, monitor, keyboard, printer, etc were used as input/output devices.
  • Some of the examples of Third Generation Computers are IBM 360, IBM 370, PDP-11, NCR 395, B6500, UNIVAC 1108, etc.

Fourth generation:

1976 to 1990: The computers of this generation used the LSI chips like microprocessors as their active electronic element. HCL Horizon III, and WIPRO’S Uniplus HCL’s Busybee PC etc.

They used a high speed microprocessor as a CPU. They were more user friendly and highly reliable systems. They had large storage capacity disk memories.

Characteristics of Fourth-Generation Computers

  • The Fourth Generation Computers have been developed using the technology of Very-large-scale integration (VLSI) and the microprocessor (VLSI has thousands of transistors on a single microchip).
  • Semiconductor memory such as RAM, ROM, etc was used for memory storage.
  • Input/output devices such as pointing devices, optical scanning, keyboard, monitor, printer, etc were introduced.
  • Some examples of Fourth Generation Computers are IBM PC, STAR 1000, APPLE II, Apple Macintosh, Alter 8800, etc.

Fifth Generation:

1990 onwards: Specialized and dedicated VLSI chips are used to control specific functions of these computers. Modern Desktop PC’s, Laptops or Notebook Computers.

The Fifth Generation of Computers has been built using the technology called Artificial Intelligence (AI). This technology encourages computers to behave like humans. Some of the applications of AI have been seen in features like voice recognition, entertainment, etc. The speed of the Fifth Generation of Computers is the highest while the sizes are the smallest. A big improvement has been noticed so far over the years in the various generations of computers in the aspect of speed, accuracy,dimensions, etc.

Characteristics of Fifth Generation of Computers

  • The 5th Generation Computers have been built based on artificial intelligence, use the Ultra Large-Scale Integration (ULSI) technology and parallel processing method (ULSI has millions of transistors on a single microchip and the Parallel processing method uses two or more microprocessors to run tasks simultaneously).
  • These computers understand natural language (human language).
  • The Fifth-generation computers are portable and smaller in size.
  • Trackpad (or touchpad), touchscreen, pen, speech input (recognize voice/speech), light scanner, printer, keyboard, monitor, mouse, etc are used as Input/Output devices.
  • Examples of 5th Generation Computers are Desktops, laptops, tablets, smartphones, etc.

Functional Unit

A computer in its simplest form comprises five functional units namely input unit, output unit memory unit, arithmetic & logic unit and control unit. Figure 2 depicts the functional units of a computer system.

 Basic functional units of a computer

Let us discuss about each of them in brief:

1. Input Unit: Computer accepts encoded information through input unit. The standard input device is a keyboard. Whenever a key is pressed, keyboard controller sends the code to CPU/Memory.

Examples include Mouse, Joystick, Tracker ball, Light pen, Digitizer, Scanner etc.

2. Memory Unit: Memory unit stores the program instructions (Code), data and results of computations etc. Memory unit is classified as:

•        Primary /Main Memory

•        Secondary /Auxiliary Memory

Primary memory is a semiconductor memory that provides access at high speed. Run time program instructions and operands are stored in the main memory. Main memory is classified again as ROM and RAM. ROM holds system programs and firmware routines such as BIOS, POST, I/O Drivers that are essential to manage the hardware of a computer. RAM is termed as Read/Write memory or user memory that holds run time program instruction and data. While primary storage is essential, it is volatile in nature and expensive. Additional requirement of memory could be supplied as auxiliary memory at cheaper cost. Secondary memories are non volatile in nature.

3. Arithmetic and logic unit: ALU consist of necessary logic circuits like adder, comparator etc., to perform operations of addition, multiplication, comparison of two numbers etc.

4. Output Unit: Computer after computation returns the  computed  results,  error messages, etc. via output unit. The standard output device is a video monitor, LCD/TFT monitor. Other output devices are printers, plotters etc.

5. Control Unit: Control unit coordinates activities of all units by issuing control signals. Control signals issued by the control unit govern the data transfers and then appropriate operations take place. Control unit interprets or decides the operation/action to be performed.

The operations of a computer can be summarized as follows:

1. A set of instructions called a program reside in the main memory of the computer.

2. The CPU fetches those instructions sequentially one-by-one from the main memory, decodes them and performs the specified operation on associated data operands in ALU.

3. Processed data and results will be displayed on an output unit.

              All activities pertaining to processing and data movement inside the computer machine are governed by a control unit.

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