1. A method of operating a computer system, said method comprising: providing a program in memory, the program including at least one program unit, each program unit comprising an Application Programming Interface (API) definition file and an implementation, each API definition file defining items in its associated program unit that are made accessible to one or more other program units, each implementation including executable code corresponding to said API definition file, said executable code including type specific instructions and data; and performing a first verification including verifying said program prior to an installation of said program, said first verification including indicating a verification error when a first program unit implementation is not internally consistent; indicating a verification error when said first program unit implementation is inconsistent with a first program unit API definition file associated with said first program unit implementation; and generating a program fault signal when a verification error is indicated.