Google is celebrating its 21st birthday today with an Doodle showing what a desktop computer looked like more than two decades ago.

The company, founded by Larry Page and Sergey Brin in 1998, traditionally marks its birthday on the Google homepage on September 27.

However, not even Google seems to really know when it was formed. Since 2006, it has celebrated its birthday on September 27, but the year before that, had it as September 26.

In 2004, its 6th birthday Doodle went online on September 7 and in the year before that, it was September 8.

In fact, none of these dates seem to have any particular relevance. The company's own history lists its incorporation date in 1998 – the nearest thing to a corporate birthday – as September 4.