The first generation of computers used:

The first generation of computers, developed from the 1940s to the 1950s, relied on Vacuum Tubes for their internal circuitry. These tubes were large, generated significant heat, consumed a lot of power, and were prone to failure, making these early computers enormous and expensive.

• Transistors replaced vacuum tubes in the second generation of computers, leading to smaller, faster, and more reliable machines.
• Integrated Circuits (ICs) characterized the third generation, further miniaturizing components and increasing processing power.
• Microprocessors emerged in the fourth generation, integrating the entire CPU onto a single chip, which paved the way for personal computers.