Intel, the world’s largest maker of computer chips, has revised its forecast for revenue in the last three months of the year, thanks to a unexpected, major improvement in demand.It says sales will be worth as much as 7.1 billion euros. Intel, which is based in California, said demand is rising world-wide, particularly for laptop computers and servers, that is the systems that run web sites and networks. Its processors power around 80% of the world’s personal computers. The company previously paid the price for misjudging the market when it was left with a stockpile of microchips worth almost 2.5 billion euros. Its share price had dropped nearly 30% this year, due to the stockpile problem and because missed sales targets and engineering and design mistakes led to the cancellation or delay of at least five major development projects. The news led to gains in the value of shares of computer chip companies worldwide, as well as those firms that make equipment to create chips.