Bill Gates was considering his eventual departure from Microsoft for two years before he made the decision public on Thursday, he said in an interview with the Financial Times.

The revelation puts a new gloss on a critical period in the company’s history during which it faced a growing challenge from Google and other internet-based companies. Microsoft’s announcement this week that Mr Gates would leave his full-time role at the company in 2008 was the first time the idea had been broached publicly. However, the Microsoft co-founder said that he had first raised the subject internally a considerable time ago, leading to long-term executive and board-level consideration of the issue.

“That goes back even a couple of years,” he said of the first time he revealed to Steve Ballmer, Microsoft’s chief executive and his former college friend, that he was thinking of leaving the company. “He’d been talking to the board for probably 18 months,” Mr Ballmer added.

The questions around the future leadership of its software development organisation came at a time when Microsoft was seeking a response to the emergence of Google, whose strategy of releasing its technology in the form of services over the internet, supported by advertising, has emerged as a powerful rival to Microsoft’s own model for developing and selling software.

Early last year, some time after Mr Gates first raised the question about his own future, Microsoft acquired Groove Networks, a small software company, and elevated its founder, Ray Ozzie, to a senior position in its own development ranks.

Mr Ozzie, who this week succeeded Mr Gates as head of Microsoft’s development organisation, was not designated as Mr Gates’s heir at the time of the acquisition.

But it soon became apparent that he would lead the response to Google. A year ago he announced a new focus on services at Microsoft, an initiative he promoted in internal memos and at public events during the rest of the year.

In March Mr Gates indicated to the board that he would make a decision on his own role at the company within three months. Mr Gates, who turned 50 last year and has led Microsoft for more than 30 years, said that age did not play a factor in his decision.

However, he added: “If you go back all the way to the early days of the company I took no vacations of any kind and I wouldn’t even read many things that didn’t have anything to do with software. I was pretty mono-maniacal and I’m not quite like that now.”