The future of Apple without Steve Jobs at its helm is hard to fathom, with experts pointing out that executives at the technology giant will now 'face big tests' in staying 'ahead of competition' and achieving 'success without Jobs in charge'.

In a surprise announcement, Apple on Thursday said Jobs has resigned as company chief executive officer and named chief operating officer Tim Cook as his successor.

Jobs will now be the chairman of Apple's board.

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"Few chief executives are as closely identified with a company as Steve Jobs has been with Apple.

"Now that he is stepping down as chief executive. . . it will largely be up to his deputies to make sure that the company continues to stay ahead of the competition with trend-setting products and services that impress consumers," a report in the Wall Street Journal said.

It said the executives that will now run Apple without Jobs will 'face big tests of whether they can still excel in highly competitive businesses that often have small profit Margins'.

The New York Times said the Apple team will face a 'far greater trial in achieving continued success without Jobs in charge'.

Stanford University's Graduate School of Business professor Charles O'Reilly said in the WSJ report one will have to wait and see if Apple 'can hit the next home run', asserting that if it doesn't, 'they're in a bunch of bad businesses'.

With a 'charismatic persona' and 'sharp instinct' for knowing what consumers want, Jobs is one of the most successful chief executives in corporate history, the New York Times said.

"The good news for Apple is that the product roadmap in this industry is pretty much in place two and three years out," the New York Times quoted Harvard Business School professor David Yoffie as saying.

"So 80 per cent to 90 per cent of what would happen in that time would be the same, even without Steve," Yoffie said.

Yoffie added that the 'real challenge for Apple will be what happens beyond that roadmap. Apple is going to need a new leader with a new way of recreating and managing the business in the future.'

Yoffie said Jobs 'had a unique combination of visionary creativity and decisiveness. No one will replace him.'

Jobs' successor, Cook, has handled the affairs of the company thrice when Jobs was on a medical leave of absence -- once in 2004 when he was recuperating from pancreatic cancer surgery, in 2009 when he was on a six-month medical leave for a liver transplant and again in early 2011 for another unexplained medical leave.

Cook isn't the showman that Jobs is, but people who know him call him an operational genius who was responsible for crafting Apple's current supply-chain system and helping to transform the company into one of the most efficient electronics manufacturers today," the WSJ report said.

Cook is known to be polite, but persistent and unyielding in his demands.

He can also absorb a huge amount of data and quickly pinpoint any problems, it added.

The Journal said Apple's recent revolutionary innovations have also been helped by deputies including Apple senior vice-president Jonathan Ive, who oversees the company's industrial design team.

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Described as one 'sharing a brain with Steve,' Ive and his group have been responsible for coming up with the physical look and feel of products that have helped set Apple apart from competitors.

The Journal said other key figures who have been a part of Jobs's inner circle for many years include Scott Forstall, who leads the team responsible for the iPhone's operating system and other software; Eddie Cue, Apple's vice-president of Internet Services, who is regarded as an 'all-purpose fixer'; and Philip Schiller, who runs world-wide marketing.

Analysts also worry that Apple could eventually be lost without Jobs's dominant personality and killer instinct.

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"Retention of the current bench may also be difficult because Apple's stock price has surged in recent years, allowing executives to make fortunes from stock options during their careers at the company and giving them less incentive to remain," the WSJ report said.

According to Michael Hawley, a professional pianist and computer scientist who worked for Jobs, Jobs' role at Apple has been more the corporate equivalent of 'an unusually gifted and brilliant orchestra conductor'.

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"Steve has done a great job of recruiting a broad and deep talent base," Hawkley said.

The New York Times said Jobs' design decisions were shaped by his understanding of both technology and popular culture.

His own study and intuition, not focus groups, were his guide.

"When a reporter asked what market research went into the iPad, Jobs had replied, "None. It's not the consumers' job to know what they want," the Times report added.