Three prominent features of first-generation computers are:

1. Vacuum Tubes

   These computers used vacuum tubes for circuitry and magnetic drums for memory. Vacuum tubes were large, fragile, and generated a lot of heat, requiring significant cooling.

2. Machine Language Programming

   Programming was done directly in machine language, which is the most basic programming language understood by computers. This made programming very difficult, time-consuming, and prone to errors.

3. Large Size and High Power Consumption

   Due to the use of thousands of vacuum tubes, first-generation computers were enormous in size, often occupying entire rooms. They also consumed vast amounts of electricity and were very expensive to operate.