Logical block addressing (LBA) is a common scheme used for specifying the location of blocks of data stored on computer storage devices, generally secondary storage systems such as hard disks. The term LBA can mean either the address or the block to which it refers. Logical blocks in modern computer systems are typically 512 or 1024 bytes each. ISO 9660 CDs (and images of them) use 2048-byte blocks. The capacity for the sector on the hard disk is usually 512 bytes.