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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: |
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no. Cylinder | (1024) |
x no. Head | ( 32) |
x no. Sector | ( 63) |
x bytes per sector | ( 512) |
| 1 GigaByte |
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