Apertures are important in address assignment. As stated in the terminology section, an aperture is an offset and range that restricts where a slave segment can be assigned in a master’s address space, that is, an assignment must fit within an aperture.
For example, if an aperture can only accept addresses from 0 to 1 G, then you cannot assign an address starting at 2 G through that aperture. Hardened processors such those found in AMD Zynq™ devices might have multiple apertures on their master interfaces.
Apertures can also come from the address width. For example, a 32-bit MicroBlaze™ processor can generate addresses from 0 to 4 G, so you cannot assign an address starting at 8 G through this aperture.