It is possible for this Definition Block to load other Definition Blocks, either statically or dynamically, where they in turn can either define new system attributes or, in some cases, build on prior definitions. Although this gives the hardware the ability to vary widely in implementation, it also confines it to reasonable boundaries. In some cases, the Definition Block format can describe only specific and well understood variances. For example, the Definition Block has built in operators for IO space. In theory, it might be possible to define something like PCI configuration space in a Definition Block by building it from IO space, but that is not the goal of the definition block.
Some operators perform simple functions, and others encompass complex functions.
The operators present are intended to allow many useful hardware designs to be easily expressed, not to allow all hardware design to be expressed. The Differentiated System Description Table is part of the system fixed description in Definition Block format. This Definition Block is like all other Definition Blocks, with the exception that it cannot be unloaded. See section 5.2.7 for a description of Definition Blocks. 5.2.7.2 Secondary System Description Table Secondary System Description Tables are a continuation of the Differentiated System Description Table.