What technology made it possible for computers to become small enough to fit on a person's desk (and later in a pocket) ?

Answer: Silicon chips

Explanation:

Silicon chips are the integrated circuit (IC) devices that are used in computing systems and devices for processing. They are made with silicon as the main element as it is available in abundant amount at low cost. It has the property of conduction as well insulation accordingly.

Gathering several silicon chips togather to make a unit of processor is the prime function. It is the component that is tending to make the computing system to size down generation by generation. Transistors are made for the devices that contain the silicon chips. If the size of transistor is decreased or the number of chips placed in transistor is decreased then the size of device also decreases. This is the major factor due to which size of technology is decreasing with the same processing.