One of the first architectural decisions that Bud and I made for the Macintosh system software in the spring of 1981 was that we were only going to try to run o

One of the first architectural decisions that Bud and I made for the Macintosh system software in the spring of 1981 was that we were only going to try to run one application at a time. We barely had enough RAM or screen space to do even that, and we thought that we'd benefit from the resultant simplifications. Besides, multi-tasking was supposed to be Lisa's forte, and we didn't want to usurp all of the reasons for buying a Lisa. --Andy Hertzfeld In the original MacOS, only one program* ran at a time. You could have multiple MacPaint windows, for example, but if you wanted to use MacDraw, you'd have to quit MacPaint. From a process point of view, this was single-tasking. Andy Hertzfeld wrote the first multi-process environment for Macintosh, "Switcher." With Switcher, you could have MacPaint and MacDraw (or any combination of as many as four apps) open simultaneously. https://www.folklore.org/StoryView.py?project=Macintosh&story=Switcher.txt https://www.folklore.org/StoryView.py?project=Macintosh&stor... Only one would control the entire screen, so if you were using MacPaint, the MacDraw (for example) windows were hidden. When you "switched" to another app, it was like side-scrolling the entire screen, the entire desktop scrolled horizontally to the left or the right and another scrolled into view. Later on, MacintoshOS (pre OS X) acquired its own cooperative multi-tasking capabilities, and when that happened, you could have multiple windows from multiple apps visible on the screen at the same time and switch by clicking on another window. It was quite the hack for its day, and had a cool UX, it was like having four Macintoshes arranged in a carouself, you could "switch" between processes. --- As another comment points out, there was another thing called a "Desk Accessory" that could co-exist on the screen with a full application. But these were not full applications and had very limited capabilities. https://www.folklore.org/StoryView.py?project=Macintosh&story=Desk_Ornaments.txt https://www.folklore.org/StoryView.py?project=Macintosh&stor...