[Someone]

> Mac OS, Win16, PalmOS all have shared heaps too

Mac OS didn’t. It had a system heap and a heap for the running application. Once it supported running multiple applications simultaneously, each of them had its own heap (https://www.folklore.org/Switcher.html: “One fundamental decision was whether or not to load all of the applications into a single heap, which would make optimal use of memory by minimizing fragmentation, or to allocate separate "heap zones" for each application. I decided to opt for separate heap zones to better isolate the applications, but I wasn't sure that was right.”)

That’s why MultiFinder had to know how much RAM to give to each application. https://en.wikipedia.org/wiki/MultiFinder#MultiFinder: “MultiFinder also provides a way for applications to supply their memory requirements ahead of time, so that MultiFinder can allocate a chunk of RAM to each according to need” (Wikipedia doesn’t mention it, but MultiFinder also allowed users to increase those settings)

[AshamedCaptain]

But isn't the system heap also a ... shared heap? It is practically the same distinction as between the global and local heaps in win16.