Just for comparison the Acorn Archimedes launched in 1987 with Arthur OS (later to become Risc OS) with a full windowed desktop with overlapping windows etc. They were able to pull this off because they had designed a new processor that they called the "Acorn RISC Machine"*

Screenshot of 1987 desktop here: https://en.wikipedia.org/wiki/History_of_RISC_OS#/media/File...

https://en.wikipedia.org/wiki/History_of_RISC_OS

* ARM for short, you might have heard of it