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 1G, then you can’t assign an address starting at 2G through that aperture. Hardened processors such those found in Zynq® devices may have multiple apertures on their master interfaces.
Apertures may also come from the address width. For example, a 32-bit MicroBlaze™ processor can generate addresses from 0 to 4G, so you cannot assign an address starting at 8G through this aperture.