Why has Nvidia driven stock markets to record highs?

Investor excitement over artificial intelligence reached a new peak this week when better-than-expected results from chipmaker Nvidia drove stock markets in three continents to record highs. The rally began on Thursday and continued into Friday, as Nvidia overtook Google's parent group, Alphabet, to become the third most valuable company in the US. Its market capitalisation hit 2tn ( 1.58tn), surpassed only by Microsoft and Apple. The artificial intelligence (AI) boom has raised many questions, not least over safety and the impact on jobs, but there are also concerns that it might be driving unsustainable market exuberance. Here we look at the latest share price rise and whether it can be maintained.