Logical Block Addressing


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Logical Block Addressing

(storage)
(LBA) A hard disk sector addressing scheme used on all SCSI hard disks, and on ATA-2 conforming IDE hard disks. The addressing conversion is performed by the hard disk firmware.

Prior to LBA, combined limitations of IBM PC BIOS and ATA restricted the useful capacity of IDE hard disks on IBM PCs and compatibles to 1024 cylinders * 63 sectors per track * 16 heads * 512 bytes per sector = 528 million bytes = 504 megabytes. Modern BIOSes select LBA mode automatically, and work around the 1024-cylinder BIOS limit by representing a hard disk to the OS as having e.g. half as many cylinders and twice as many heads. However, there is still an unbreakable BIOS disk size limit of 1024 cylinders * 63 sectors per track * 256 heads * 512 bytes per sector = 8 gigabytes, but modern OSes (including Windows 9x, Windows NT and Linux) are not affected by it, since they issue direct LBA-based calls, bypassing the BIOS hard disk services completely.
References in periodicals archive ?
The new SL82C105 supports up to four disk drives, new faster data transfer modes (PIO mode 3, 4 and 5 and DMA modes 0, 1 and 2), and supports Logical Block Addressing (LBA), allowing hard drive capacity of up to 8 gigabytes.
The new SL82C105 supports up to four disk drives, new faster data transfer modes (PIO mode 3,4 and 5 and DMA modes 0,1 and 2), and supports Logical Block Addressing (LBA), allowing hard drive capacity of up to 8 gigabytes.
Maxtor's EIDE interface is compliant with the American National Standard Institute (ANSI) ATA-2 specification and includes Logical Block Addressing capability to break the 528MB PC capacity barrier.