The Java VM is like a virtual processor --- it lets you run an ordinary program that's written in Java bytecode. The Smalltalk VM is like a machine emulator --

The Java VM is like a virtual processor --- it lets you run an ordinary program that's written in Java bytecode. The Smalltalk VM is like a machine emulator --- it runs a complete Smalltalk system, complete with its own screen, GUI, multiple processes and concurrent programs, IDE, debugger, editor, etc, all mixed together. This typically all runs inside a single window, with its own windowing system. It's a hangover from the days when Smalltalk would run on the bare metal of a computer --- it was the entire operating system.