Bill Gates focused Microsoft on developing applications for computers with graphical user interface in this 1983 internal strategy memo.

June 1983

Excerpt from memo written by Bill Gates and Steve Ballmer

Microsoft believes in mouse and graphics as invaluable to the man-machine interface. We will bet on that belief by focusing new development on the two new environments with mouse and graphics … Macintosh and Windows.

This also makes sense from a marketing perspective. Our focus will be on the business user, a customer who can afford the extra hardware expense of a mouse and high resolution screen, and who will pay premium prices for quality easy-to-learn software.

Microsoft will not invest significant development resources in new Apple II, MSX, CP/M-80 or character-based IBM PC applications. We will finish development and do a few enhancements to existing products.

… Over the foreseeable future our plan is to implement products first for the Mac and then to port them to Windows. We are taking care in the design of the Windows user interface to make this as easy as possible.

Source: “Gates: how Microsoft’s mogul reinvented an industry — and made himself the richest Man in America.” Stephen Manes and Paul Andrews. 1993.