Don't argue with me. $100k is fair, and you know it

Andy Hertzfeld traces the idea for Switcher, the Macintosh’s first multitasking environment, to an October 1984 demonstration of Thunderscan. When Byte reviewer John Markoff rapidly moved between programs on an IBM PC, Hertzfeld saw how a similar utility could make the new 512K Macintosh more useful. He began sketching a design while finishing Thunderscan, weighing a shared memory heap against separate heaps for each application. He favored separate heaps for better isolation, while recognizing that switching applications would also require saving and restoring numerous system variables.

Microsoft independently wanted the same capability. Its team believed a switcher would preserve the advantage of its compact Macintosh applications: users could keep more of them available at once, despite the larger memory of the 512K model and Lotus’s integrated Jazz suite. Bill Gates tried to estimate the work at under ten weeks and $40,000, using an assumed coding rate to press Hertzfeld toward a low fee. Hertzfeld declined to negotiate before knowing whether the concept would work, and argued that a successful switcher belonged with the Macintosh system rather than under Microsoft’s control. He nevertheless promised to make it work well with Microsoft software. Back home, excited by the challenge, he began a proof-of-concept program before completing his other project; the prototype was hardwired to switch among MacPaint, MacWrite, MacDraw, and the Finder.