Abstract: A data processing system and method include an address space which is controlled by a memory management unit and which is treated as being divided into main-sections (chunks) and sub-sections (grains). The grains may be configured to be of one of a selected number of sizes. Irrespective of the grain size, there is a fixed number of grains within each chunk. A bank of grain registers 20 stores access control parameters for each grain. In operation, a memory address (va?31:0!) is decoded to determine which chunk it relates to so that the grain size for that chunk may be determined. Having determined the grain size, the rest of the address may be decoded to pick out the grain in which the address is located, and then the access control parameters for that grain are recovered.