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If user set his HDD to NORMAL mode, the maximum accessible HDD size will
be 528 Megabytes even though its physical size may be greater than that!
LBA (Logical Block Addressing) mode: A new HDD accessing method to
overcome the 528 Megabyte bottleneck. The number of cylinders, heads &
sectors shown in 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 & 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 sector ( 512)
8.4 GigaBytes
LARGE mode: Extended HDD access mode supported by Award Software.
Some IDE HDDs contain more than 1024 cylinder without LBA support (in some
cases, user do not want LBA). 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. A
reverse 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 GigaByte