Chapter 3
KuDoz 7X
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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
transformation 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 num-
ber of cylinders, heads and sectors shown in setup may not be the number physi-
cally contained in the HDD.
During HDD accessing, the IDE controller will transform the logical address de-
scribed 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.
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