A method for address mapping, comprising: providing a mapping unit (303; 503; 603; 703; 803; 903; 1003) having logical to physical mapping data corresponding to a fixed range of non-overlapping logical addresses, the mapping unit having a data unit type associated therewith, wherein the data unit type defines the particular amount of physical data to which a quantity of logical to physical mapping entries correspond, and wherein the data unit type is variable such that the amount of physical data to which the quantity of logical to physical mapping entries correspond is variable; characterised by: said mapping unit comprising both: a first portion (305; 405; 505; 605; 705; 805; 905; 1005) comprising mapping data comprising the quantity of logical to physical mapping entries each corresponding to a particular amount of physical data stored on a memory (110; 510; 610; 710; 810), wherein the quantity of logical to physical mapping entries depends on a data unit size defined by the data unit type; and a second portion (307; 407; 507; 607; 707; 807; 907; 1007) comprising: mapping data indicating locations on the memory (110; 510; 610; 710; 810) of a plurality of other mapping units (303; 503; 603; 703; 803; 903; 1003) of a mapping unit group (409; 509; 609; 709; 809; 909) to which the mapping unit belongs; and attribute data indicating the data unit type associated with the mapping units of the mapping unit group; and said mapping units of the plurality of other mapping units each comprise: a first fixed amount of space (605-i) allocated for a data unit mapping table (615-i); and a second fixed amount of space (607-i) allocated for a mapping unit mapping table; wherein the data unit mapping table (615-i) of at least one of the plurality of other mapping units uses less than the first fixed amount of space (605-i) allocated for the data unit mapping table (615-i) and comprises: a first quantity of logical to physical mapping entries (611-i) mapping to physical data units having a size defined by a data unit type of the respective mapping unit; and a second quantity of logical to physical mapping entries (619-i) mapping to physical data units having a size other than the size defined by the data unit type of the respective mapping unit; and wherein said data unit type comprises: at least one data unit type that corresponds with a particular amount of physical data that is less than a physical page size corresponding to a memory device to which the data is mapped, and at least one data unit type that corresponds with a particular amount of physical data that is greater than a physical page size corresponding to a memory device to which the data is mapped. said mapping unit comprising both: a first portion (305; 405; 505; 605; 705; 805; 905; 1005) comprising mapping data comprising the quantity of logical to physical mapping entries each corresponding to a particular amount of physical data stored on a memory (110; 510; 610; 710; 810), wherein the quantity of logical to physical mapping entries depends on a data unit size defined by the data unit type; and a second portion (307; 407; 507; 607; 707; 807; 907; 1007) comprising: mapping data indicating locations on the memory (110; 510; 610; 710; 810) of a plurality of other mapping units (303; 503; 603; 703; 803; 903; 1003) of a mapping unit group (409; 509; 609; 709; 809; 909) to which the mapping unit belongs; and attribute data indicating the data unit type associated with the mapping units of the mapping unit group; and mapping data indicating locations on the memory (110; 510; 610; 710; 810) of a plurality of other mapping units (303; 503; 603; 703; 803; 903; 1003) of a mapping unit group (409; 509; 609; 709; 809; 909) to which the mapping unit belongs; and attribute data indicating the data unit type associated with the mapping units of the mapping unit group; and said mapping units of the plurality of other mapping units each comprise: a first fixed amount of space (605-i) allocated for a data unit mapping table (615-i); and a second fixed amount of space (607-i) allocated for a mapping unit mapping table; a first fixed amount of space (605-i) allocated for a data unit mapping table (615-i); and a second fixed amount of space (607-i) allocated for a mapping unit mapping table; a first quantity of logical to physical mapping entries (611-i) mapping to physical data units having a size defined by a data unit type of the respective mapping unit; and a second quantity of logical to physical mapping entries (619-i) mapping to physical data units having a size other than the size defined by the data unit type of the respective mapping unit; and at least one data unit type that corresponds with a particular amount of physical data that is less than a physical page size corresponding to a memory device to which the data is mapped, and at least one data unit type that corresponds with a particular amount of physical data that is greater than a physical page size corresponding to a memory device to which the data is mapped.