Which major technological advancement characterizes the fourth generation of computers?

The correct option is Microprocessors.

Computers are categorized into five distinct generations based on the core technological advancements used in their design and construction:

• First Generation (1940s–1950s): Used Vacuum tubes for circuitry and magnetic drums for memory.
• Second Generation (1950s–1960s): Replaced vacuum tubes with Transistors, making computers smaller, faster, and more energy-efficient.
• Third Generation (1960s–1970s): Introduced Integrated Circuits (ICs), placing hundreds of transistors onto a single silicon chip.
• Fourth Generation (1970s–Present): Characterized by the development of the Microprocessor (VLSI and ULSI circuits), which placed thousands to millions of integrated circuits onto a single microchip (CPU).
• Fifth Generation (Present & Beyond): Built around Artificial Intelligence (AI), parallel processing, and super conductors.

Therefore, microprocessors represent the defining technology of the fourth generation of computers.