3-18 CHAPTER 3
LBA (Logical Block Addressing) mode
A new HDD accessing method to overcome the 528 Megabyte bottleneck. The
number of cylinders, heads and sectors shown in the setup may not be the number
physically contained in the HDD.
During HDD accessing, the IDE controller will transform the logical address
described by sector, head and cylinder into its own physical address inside the HDD.
The maximum HDD size supported by LBA mode is 8.4 Gigabytes which is
obtained by the following formula:
no. Cylinder (1024)
x no. Head ( 255)
x no. Sector ( 63)
x bytes per secttor ( 512)
8.4 Gigabytes
LARGE mode
Extended HDD access mode is supported by Award Software.
Some IDE HDDs contain more than 1024 cylinder without LBA support (in some
cases, users do not want the LBA mode). The Award BIOS provides another
alternative to support these kinds of LARGE mode:
CYLS. HEADS SECTOR MODE
1120 16 59 NORMAL
560 32 59 LARGE
BIOS tricks DOS (or other OS) that the number of cylinders is less than 1024 by
dividing it by 2. At the same time, the number of heads is multiplied by 2. Areverse
transformation process will be made inside INT 12h in order to access the right
HDD address.
Maximum HDD size:
no. Cylinder (1024)
x no. Head ( 32)
x no. Sector ( 63)
x bytes per sector ( 512)
1 Gigabytes