The memory interface of AMD K8 CPUs supports "Extended fixed-range MTRR Type-Field Encodings" which allows one to specify whether accesses to certain address ranges are executed by accessing RAM through the Direct Connect Architecture or by executing memory-mapped I/O.
AMD K8 CPU's memory interface offers a mechanism called "Extended fixed-range MTRR Type-Field Encodings" that allows users to control how specific address ranges are accessed, either directly through RAM (using the Direct Connect Architecture) or via memory-mapped I/O.