Last week,Bill Gates retired from full-time work at the world's biggest computer software company, Microsoft.He will remain chairman of the company he established with Paul Allen in nineteen seventy-five. Mister Gates leaves Microsoft at a time of change in the computing industry.Microsoft grew at a time when personal computers,or PCs,were replacing big mainframe computers as the main computing tools.He showed that huge profits could be made in software as PCs increasingly were found "on every desk and in every home."  Early on,Microsoft understood the importance of the "network effect." That is, software is the kind of product that increases in value as more people buy and use it.  Now,free Internet software threatens to replace PC-based software.Devices like "smart phones" connect people to the Internet.Google has become a 1eader in Internet Web searching and advertising.Microsoft has struggled to change with the new computer environment.Its efforts to sell music and its latest operating system,Vista,have not been big successes.And an attempt this year to buy Yahoo for over forty-seven billion dollars failed.  In the last several years,Bill Gates has slowly given control of Microsoft to others.In two thousand,he gave the job of chief executive officer to Steve Ballmer, a friend of his since their years at Harvard University.Mister Ballmer has been with Microsoft since nineteen eighty.Still,it is hard to overestimate  the influence of Bill Gates on computing.He developed the business model that put the Windows operating system on about ninety percent of the world's one billion PCs.Microsoft now has almost ninety thousand employees.  At fifty--two years old,Bill Gates is currently the third richest man in the world.He is worth about fifty-eight billion dollars.He remains Microsoft's biggest shareholder.  Mister Gates will now spend most of his time working at his charity organization, the Bill and Melinda Gates Foundation.The foundation is the world's largest charity with over thirty-seven billion dollars.It provides money for health, education and other projects,mostly in developing countries. Bill Gates retired from full-time work in Microsoft because
he had earned enough money Google threatened Microsoft's leading place PCs were out of fashion of a reason that was not mentioned