A Definition Block can be loaded from system memory address space. One use of a Definition Block is to describe and distribute platform version changes. Definition blocks enable wide variations of hardware platform implementations to be described to the ACPI-compatible OS while confining the variations to reasonable boundaries. Definition blocks enable simple platform implementations to be expressed by using a few well-defined object names. In theory, it might be possible to define a PCI configuration space-like access method within a Definition Block, by building it from IO space, but that is not the goal of the Definition Block specification.
Some operators perform simple functions and others encompass complex functions.
The operators present are intended to allow many useful hardware designs to be ACPI-expressed, not to allow all hardware design to be expressed.