After graduating magna cum laude in Computer Science in June 1978 from the University of Washington he designed a schematic of Microsoft's Z-80 SoftCard which had a Z80 CPU and ran the CP/M operating system on an Apple II.
A month later, with the release of the 8086 CPU, Paterson designed the S-100 8086 board, which could only run a standalone version of Microsoft BASIC, so to compensate he designed QDOS (Quick And Dirty Operating System), which was a rough port of CP/ API code, eventually called 86-DOS
Microsoft secured marketing rights to 86-DOS December 1980.
He actively worked for Microsoft May 1981-1982 as a programmer, left to form Falcon Technology (bought by Microsoft in 1986), then worked two more employment tenures with Microsoft Corporation from 1986-1988 and 1990-1998 respectively, writing the code for Visual Basic during this last term of employment.
He is no longer employed by Microsoft.