Bit 4 - LBA translation

If the system is configured for LBA type addressing, this bit is set to 1. When LBA translation is on, the Extended Int 13h interface (Fn 41h-48h) pass LBA values directly to the device. The conventional Int 13h interface ignores this bit and always uses CHS. LBA-type addressing is available on drives with less than 1024 cylinders, and therefore bit 3 (CHS translation) is independent from bit 4 (LBA translation).