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Many people enjoy a misconception that all larger computers are from older generations and small computers are the fourth generation computers. Remember, computers are classified into different generations NOT based on their sizes. Though it is true that the old computers were compelled to be of bigger size (larger components and lack of advanced technology).
The vacuum tubes used in first generation were replaced by transistors in second and which in turn were replaced by ICs (Integrated Circuits) in third generation computers. So, first of all, let’s look at those ICs.
Integrated Circuit (IC) is a small electronic device made out of semiconductor material. The first integrated circuit was developed in the 1950s by Jack Kilby of Texas Instruments and Robert Noyce of Fairchild Semiconductor. – WeboPedia
It is amusing to know that two people thought about the same solution but independently. There is the interesting story about how Robert Noyce got the patent.
Please check R.C. Khanal’s ‘Computer Concept‘ book. He has nicely explained how these IC Chips are manufactured in ‘Computer Generations’ chapter. Notice the terms silicon, wafers, and photolithography.
So, after the invention of IC Chips, it is possible to integrate thousands of registers, diodes, capacitors and many other electronic components and circuitry in a tiny chip.
Integrated circuits are referred with different names like Chips, ICs, Microchips, and so on.
A tiny chip contains the whole electronic network that performs complex tasks.
The computers using small scale integration circuits (SSI)and medium scale integration circuits (MSI) are under this class. The invention of IC Chips made it possible to greatly reduce the size of computers with improvement in operation speed (nanoseconds) and reliability.
The most noticeable achievement of third generation is the development of operating systems. The operating systems allowed the machines to run many different applications. These applications were monitored and coordinated by the computer’s memory.
In 1969 AT&T Bell Laboratories programmers Kenneth Thompson and Dennis Ritchie developed the UNIX operating system on a spare DEC minicomputer. UNIX was the first modern operating system that provided a sound intermediary between software and hardware. UNIX provided the user with the means to allocate resources on the fly, rather than requiring the resources be allocated in the design stages. The UNIX operating system quickly secured a wide following, particularly among engineers and scientists at universities and other computer science organizations.
User interface devices such as Keyboards and Monitors started from this generation. Similarly, GUI also was started from third generation. These are important development of third generation of computers.