A wave of job losses has started to spread across Silicon Valley as the trademark optimism of the region's technology start-ups has turned quickly to pessimism amid the financial market rout.

The rapid reversal in mood has reawakened memories of the dotcom bust in 2001 - though the entrepreneurs making the redundancies claim a much greater sense of realism than was shown during the first great internet shake-out, when many web companies reacted far too late to the downturn.