Moore's Law states that the number of integrated circuits in a CPU doubles every 18 months.
This "law" was named after Dr. Gordon E. Moore, cofounder of Intel Corporation. Originally, this was an observation he wrote in his article in the April 19, 1965 issue of "Electronics" magazine, in which he describes the general progress of integrated circuits. His original estimate was 12 months, then ten years after he wrote the article, he changed it to 24 months. Since then others - not Moore - have split the difference to 18 months. When it became apparent that his observation was becoming more accurate, they simplified his observation and called it Moore's Law. And people have been applying Moore's Law to everything from clock frequency to the number of transistors in a CPU of any printed circuit board.
According to Moore's Law, the Pentium 4 should reach the 2.8GHz speed from the current 1.4GHz in 18 months.