Manual for BA1 series
Chapter 3
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The Award BIOS supports 3 HDD modes: NORMAL, LBA and LARGE.
CHS mode
Generic access mode in which neither the BIOS nor the IDE controller will make any trans-
formation during accessing. The maximum number of cylinders, heads and sectors for CHS
mode are 1024,16 and 63.
If the user sets 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 and 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 and cylinder number into its own physical address inside the HDD.
Large mode
Some IDE HDDs contain more than 1024 cylinder without LBA support (in some cases,
users do not want LBA). The Award BIOS provides another alternative to support these
kinds of HDD.
BIOS tricks DOS (or other OS) into divising 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 INT13h in order to access the right HDD address.
If using Auto detect, the BIOS will automatically detect the IDE hard disk mode and set it as
one of the three modes.
Remark
To support LBA or LARGE mode of HDDs, there must be some softwares involved which
are located in Award HDD Service Routine(INT13h).It may fail to access a HDD with LBA
(LARGE) mode selected if you are running under an Operating System which replaces the
whole INT 13h.
