The Common Language Implementation (CLIM) subsystem contains the classes and associated methods which, together with the virtual machine, implement the Smalltalk class and message mechanisms. In most cases, the implementation of CLIM is inseparably tied to the virtual machine and includes Behavior, Class, Compiler, and CompiledMethod. (The virtual machine is the program that provides the Smalltalk execution environment on a single machine. It maps data and logic to the executing machine architecture, isolating the Smalltalk code from the architecture of the machine.)