Logical Block Addressing
Logical Block Addressing
(storage)Prior to LBA, combined limitations of IBM PC BIOS andATA restricted the useful capacity of IDE hard disks on IBMPCs and compatibles to 1024 cylinders * 63 sectors per track *16 heads * 512 bytes per sector = 528 million bytes = 504megabytes. Modern BIOSes select LBA mode automatically, andwork around the 1024-cylinder BIOS limit by representing ahard disk to the OS as having e.g. half as many cylinders andtwice as many heads. However, there is still an unbreakableBIOS disk size limit of 1024 cylinders * 63 sectors per track* 256 heads * 512 bytes per sector = 8 gigabytes, but modernOSes (including Windows 9x, Windows NT and Linux) arenot affected by it, since they issue direct LBA-based calls,bypassing the BIOS hard disk services completely.