the most common physical sector size for harddisks today is 512 bytes, but there have been hard disks with 520 bytes per sector as well for non-ibm compatible machines. in 2005 some seagate custom hard disks used sector sizes of 1024 bytes per sector. advanced format hard disks use 4096 bytes per physical sector (4kn) since 2010, but will also be able to emulate 512 byte sectors (512e) for a transitional period.