1. A processing unit, comprising: a memory; an arithmetic logic unit; and control logic having access to program instructions of a control store, said control logic comprising logic to: access multiple sets of variables, variables in the different sets of variables being identically referenced by instructions; associate a one of the sets of variables as a current set of variables to be used in instructions that are executed by the arithmetic logic unit; automatically change the set of variables associated with the current set of variables in response to a procedure call; automatically change the set of variables associated with the current scope in response to a procedure exit; and alter the value of a variable of a set of the variables other than the set of variables associated with the current set of variables in response to an instruction.