See the Design Principles Behind Smalltalk article: https://www.cs.virginia.edu/~evans/cs655/readings/smalltalk.html https://www.cs.virginia.edu/~evans/cs655/re

See the Design Principles Behind Smalltalk article: https://www.cs.virginia.edu/~evans/cs655/readings/smalltalk.html https://www.cs.virginia.edu/~evans/cs655/readings/smalltalk.... Some relevant excerpts: Here are some examples of conventional operating system components that have been naturally incorporated into the Smalltalk language: [...] Display handling -- The display is simply an instance of class Form, which is continually visible, and the graphical manipulation messages defined in that class are used to change the visible image. [...] Debugger -- The state of the Smalltalk processor is accessible as an instance of class Process that owns a chain of stack frames. The debugger is just a Smalltalk subsystem that has access to manipulate the state of a suspended process. It should be noted that nearly the only run-time error that can occur in Smalltalk is for a message not to be recognized by its receiver. Smalltalk has no "operation system" as such. The necessary primitive operations, such as reading a page from the disk, are incorporated as primitive methods in response to otherwise normal Smalltalk messages. This is from 1981, BTW.