Apple founder Steve Jobs has resigned as chief executive of the technology giant and will be replaced by its chief operating officer Tim Cook.

苹果创始人史蒂夫·乔布斯辞去董事长一职，首席运营官蒂姆·库克将代替他的职位。

Mr Jobs had been on his third medical leave since announcing his cancer diagnosis seven years ago
Mr Jobs, who underwent a liver transplant following pancreatic（胰腺） cancer, said he could no longer meet his chief executive's duties and expectations.

The Silicon Valley legend will become chairman of the firm.

The 56-year-old has been on medical leave for an undisclosed condition since 17 January.

In a short letter to the board of Apple, Mr Jobs wrote: "I have always said if there ever came a day when I could no longer meet my duties and expectations as Apple's chief executive, I would be the first to let you know.

"Unfortunately, that day has come. I hereby resign as chief executive of Apple.

"I believe Apple's brightest and most innovative days are ahead of it. And I look forward to watching and contributing to its success in a new role.

"I have made some of the best friends of my life at Apple, and I thank you all for the many years of being able to work alongside you."

Apple board member Art Levinson paid tribute to Mr Job's contribution to the company: "Steve's extraordinary vision and leadership saved Apple and guided it to its position as the world's most innovative and valuable technology company."

'Hugely successful'

Analysts said the move was not unexpected, and would have little impact on the day-to-day running of the company.

"Steve is [still] going to be able to provide the input he would do as a chief executive," said Colin Gillis at BGC Financial.

"But Tim has been de facto（实际上的） chief executive for some time and the company has been hugely successful. The vision and the roadmap is intact."

Nor will customers see any real difference, analysts said.

"At the end of the day, consumers don't buy products from Apple because they're from Steve Jobs, they buy them because they meet their needs and they're good products, and they'll continue to do that," Michael Gartenberg from Gartner told the BBC.

However, Apple shares slid more than 5% in after-hours trading, suggesting that some investors were less confident of the company's prospects without Mr Jobs at the helm.

At the same time, shares in two of Apple's main Asian rivals gained. Taiwan-based phone maker HTC rose 4.1%, while South Korea's Samsung Electronics gained 3.2%.

The firms compete with Apple in the smartphone and tablet-PC sector, and have been involved in legal battles with Apple over patent rights. Analysts said that Mr Jobs' departure may make life easier for rivals.

"Maybe this will make the playing field a bit more level," Bryan Ma of IDC Asia-Pacific told the BBC's Asia Business Report.