Provided is a method, system, and article of manufacture for providing an address format compatible with different addressing formats used for addressing different sized address spaces. An address format is used in an operating system to address storage space in a storage device comprising a first region and a second region of storage space. A first group of applications uses the address format to only address the storage space in the first region and is not coded to use the address format to access the second region and a second group of applications uses the address format to address the storage space in the first and second regions.