> Smalltalk UIs used to work with only one CPU thread. Any action from the user would freeze the whole UI while it was working …

If that happened maybe a programmer messed-up the green threads!

"The Smalltalk-80 system provides support for multiple independent processes with three classes named Process, ProcessorScheduler, and Semaphore. "

p251 "Smalltalk-80 The Language and it's Implementation"

https://rmod-files.lille.inria.fr/FreeBooks/BlueBook/Blueboo...