[itishappy]

Rough guess: mid 1980s

4004 from the 1970s used 2300 transistors, so it would have needed to sell billions.

Pentium from 1990s had 3M transistors, so it could hit our target by selling a million units.

I'm betting (without much research) that the Pentium line alone sold millions, and the industry as a whole could hit those numbers about 5 years earlier.