In the second generation of computers, transistors were used instead of vacuum tubes. These transistors were smaller and of compact size than the vacuum tubes and cheaper in cost. They consumed less power and more reliable.

The second generation of computers consisted of transistors.

Explanation:
Advancements in technology led to the development of the second generation of computers, which saw a significant improvement in their performance and capabilities compared to the first generation. The key component that defined this generation was the use of transistors.

1. Transistors:
- Transistors are small electronic devices that can amplify or switch electronic signals and electrical power.
- They were invented in the late 1940s and replaced the bulky vacuum tubes used in the first generation of computers.
- Transistors were much smaller, more reliable, and consumed less power than vacuum tubes, making them ideal for use in computers.
- They were made from semiconducting materials like silicon or germanium and could be mass-produced.

Advantages of Transistors:
- Transistors were faster, more efficient, and more reliable than vacuum tubes.
- They generated less heat and consumed less power, which helped in reducing the size and cost of computers.
- The use of transistors allowed for the development of smaller and more compact computer systems.

Other Components:
- While transistors were the most significant advancement, other components such as diodes and chips were also used in second-generation computers.
- Diodes are electronic devices that allow current to flow in one direction and block it in the other.
- Chips, or integrated circuits, are miniaturized electronic circuits that combine multiple electronic components on a single semiconductor material.
- VLSI (Very Large Scale Integration) microprocessors, which are chips with a very high number of transistors, were not widely used in the second generation but became prominent in the third generation.

Conclusion:
In summary, the second generation of computers primarily consisted of transistors. These smaller, faster, and more reliable electronic devices replaced the bulky vacuum tubes of the first generation. Although other components such as diodes and chips were also used, transistors were the defining feature of second-generation computers.