1. A computer system comprising: a processor; a memory coupled to the processor including a first memory address space and a second memory address space; an interface coupled to the memory to access the first memory address space when the processor is operating in a first mode and to access the second memory address space when the processor is operating in a second mode; a request line coupled to the interface, the request line designating a signal requesting operation of the processor in the second mode when there is a need to make a real-mode call during operation in the first mode; and logic to transfer operation of the processor to the second mode to make the real-mode call and transfer operation of the processor back to the first mode after the real-mode call is executed.