The correct answer is (a).
The first generation of computers was designed using vacuum tubes. Vacuum tubes are a type of electronic valve that was used to amplify and switch electronic signals and electrical power. They were the first electronic devices to be used in computers, and they were used in all computers from the 1940s to the early 1950s.
Vacuum tubes are large, bulky, and power-hungry. They also generate a lot of heat, which can cause them to fail. For these reasons, vacuum tubes were eventually replaced by transistors in the second generation of computers.
Transistors are a type of semiconductor device that can be used to amplify and switch electronic signals and electrical power. They are much smaller and more efficient than vacuum tubes, and they do not generate as much heat. For these reasons, transistors replaced vacuum tubes in all computers from the early 1950s to the late 1960s.
The third generation of computers was designed using integrated circuits. Integrated circuits are a type of electronic circuit that is made up of many transistors and other electronic components that are etched onto a single piece of semiconductor material. Integrated circuits are much smaller and more powerful than transistors, and they are also much more reliable. For these reasons, integrated circuits replaced transistors in all computers from the late 1960s to the early 1980s.
The fourth generation of computers was designed using microprocessors. Microprocessors are a type of integrated circuit that contains the central processing unit (CPU) of a computer. Microprocessors are much smaller and more powerful than integrated circuits, and they are also much more reliable. For these reasons, microprocessors replaced integrated circuits in all computers from the early 1980s to the present day.