Gates drops out of Harvard and moves to Albuquerque, New Mexico, to work full-time at MITS. He and Allen officially found Microsoft (originally Micro-Soft) on April 4, 1975. Their initial focus is on developing software for the Altair.

Microsoft relocates its headquarters to Bellevue, Washington, closer to Gates's family and potential talent pool.

Microsoft secures a pivotal contract with IBM to develop the operating system for IBM's new personal computer. Microsoft purchases QDOS (Quick and Dirty Operating System) from Seattle Computer Products, adapts it, and licenses it to IBM as PC-DOS. This decision allows Microsoft to license the OS to other manufacturers, establishing a dominant position in the PC market.

IBM PC is launched with MS-DOS, propelling Microsoft's rapid growth and establishing it as a key player in the burgeoning PC industry.

Microsoft releases Windows 1.0, a graphical user interface (GUI) for MS-DOS. While initially slow to gain traction, it lays the foundation for future Windows versions.

Microsoft goes public, making Gates a multi-millionaire overnight. The initial public offering (IPO) marks a turning point in the company's history.

Windows becomes the dominant operating system for personal computers, solidifying Microsoft's position as a global leader in the software industry. Microsoft launches Windows 95, a major upgrade that further simplifies the user interface and integrates networking features.

Initially slow to recognize the potential of the Internet, Microsoft pivots and launches Internet Explorer, engaging in a fierce browser war with Netscape. They also create MSN (Microsoft Network) a web portal.

The United States Department of Justice files an antitrust lawsuit against Microsoft, alleging that the company used its dominance in the operating system market to stifle competition in the browser market. The case lasts for several years and results in a settlement.