Logical Block Addressing (LBA)

Defines the addressing of the device by the linear mapping of sectors. The Logical Block Address (LBA) mode can only be utilized in systems that support this form of translation. The Cylinder, Head and Sector (CHS) geometry of the drive, as presented to the host, differs from the actual physical geometry.

The host AT computer may access a drive of set parameters; number of cylinders, heads and sectors per track, plus cylinder, head and sector addresses. However, the drive can't use these host parameters directly because of zone density recording techniques. The drive translates the host parameters to a set of logical internal addresses for data access.

The host drive geometry parameters are mapped into an LBA based on this formula:

LBA = (HSCA - 1) + HHDA x HSPT + HNHD x HSPT x HCYA   (1)

       = (HSCA - 1) + HSPT x(HHDA + HNHD x HCYA)              (2)

Where:  
HSCA = Host Sector Address
HHDA = Host Head Address
HCYA = Host Cylinder Address
HNHD = Host Number of Heads
HSPT = Host Sector Per Track

The LBA is checked for violating the drive capacity. If it does not, the LBA is converted to physical drive cylinder, head and sector values. The physical address is then used to access or store the data on the disk and for other drive related operations.

Close Window