Which of the following hardware was used by the first-generation computers?

First-generation computers used vacuum tubes as their switching and amplifying components.

These machines were huge, drew heavy power and gave off much heat, and the tubes failed often.

Transistors belong to the second generation, being smaller and more reliable replacements for tubes.

Integrated circuits mark the third generation, placing many transistors onto a single chip.

VLSI defines the fourth generation, packing very large numbers of components onto one microchip.

The famous ENIAC of the first generation held nearly eighteen thousand vacuum tubes.