Bill Gates' drive to put a computer on every office desktop and home helped change the way computer software was written, ultimately making him the richest man in the world. Programming at age 13, he developed a version of BASIC for the MITS Altair, considered the first microcomputer, before he dropped out of Harvard in 1975. With Paul Allen, he then created Microsoft, now the world's largest software company. Their trick was tweaking a computer operating system called Q-DOS, which Microsoft bought from Seattle Computer Products. Although it was clunky, everyone needed an operating system to run computers. Then in May 1990, Microsoft Windows 3.0 with graphical interfaces and drop-down windows appeared. Other areas dominated by Microsoft include software applications with its Excel for spreadsheets, Word for word processing, and Access for databases. Gates wrote two books, Business @ the Speed of Thought and The Road Ahead, with proceeds going to education-based non-profit organizations. Also, the Bill and Melinda Gates Foundation has donated more than $24 billion to support philanthropic programs.