Fixed-block architecture (FBA) is an IBM term for the hard disk drive (HDD) layout in which each addressable block (more commonly, sector) on the disk has the same size, utilizing the well-established three-number block addressing scheme. FBA as a term was created and used by IBM for its HDDs beginning in 1979 to distinguish such drives as IBM transitioned away from their variable record size format used on IBM's mainframe hard disk drives beginning in 1964 with its System/360; later, FBA evolved into the logical block addressing (LBA), which is a linear block addressing scheme for the fixed length blocks.