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

• Beyond the fourth generation

First generation: 1946 to 1955: Computers of this generation used Vacuum Tubes. The computes were built using 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 life time and limited programming facilities.

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.

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. Fourth generation: 1976 to 1990: The computers of this generation used the LSI chips like microprocessor as their active electronic element. HCL horizen III, and WIPRO’S Uniplus+ HCL’s Busybee PC etc. They used high speed microprocessor as CPU. They were more user friendly and highly reliable systems. They had large storage capacity disk memories.

Beyond Fourth 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