Which among the following generation computers had expensive operation cost?

Computers are grouped into generations based on the core technology used to build them, and this technology strongly affected their cost, size, and reliability.

First generation computers were built using vacuum tubes. Vacuum tubes consumed enormous amounts of electrical power, generated a great deal of heat, required constant cooling, and failed frequently, which meant they needed continuous maintenance and replacement parts. All of this made first generation computers extremely expensive to keep running.

Later generations moved to transistors (second generation), integrated circuits (third generation), and microprocessors (fourth generation), each of these advances reduced power consumption, heat output, size, and the frequency of failures, which steadily lowered running costs compared to the vacuum-tube-based first generation machines.

Exam tip: link vacuum tubes directly to the first generation, and remember that their high power use, heat, and failure rate is exactly why running them was so expensive.