Now, a report in industry mag MCV says that milestone has officially been reached.
“We’ve already surpassed the installed base of the original Xbox – which is a really significant milestone. We’ve been blown away by the appetite of people to consumer digital entertainment experiences," said Chris Lewis, Microsoft VP of Interactive Entertainment Business for Europe, the Middle East and Africa.
Xbox 360 hit the mark in about three years. The original Xbox took around five years to sell the same amount.
In September, Microsoft made significant price cuts to the Xbox 360, which the company says has helped broaden its audience.
You can read more from Microsoft's Lewis in this Edge interview.