According to NBC, as of Tuesday's close, Microsoft was worth $749 billion, and Alphabet's market capitalisation stood at $739 billion. Google went public in 2004 and spent the next eight years closing the gap with Microsoft, which debuted on the stock market in 1986. Even after Google first passed Microsoft in 2012, the companies flip-flopped several times over the next few years.

Microsoft's latest rally has been sparked by growth in its cloud computing business, which is bigger than Google's though it still trails Amazon Web Services. In March, Microsoft reorganised its Windows and Devices Group and moved its engineering resources into other units, including one focusing on cloud and artificial intelligence. Both Microsoft and Alphabet beat analysts' expectations in the first quarter.

The Tame Apple Press points out that Microsoft still trails behind Apple's market valuation of $923 billion and Amazon's $782 billion market cap. However, some analysts are sitting waiting for the Apple bubble to burst as it has not come up with a new or even marketably different product for some time.  Amazon, on the other hand is growing stronger too.