The day before yesterday, a net friend asked about the three hard disk working modes, so I wrote down a little knowledge on this topic; in the motherboard BIOS everyone can see hard disk mode options such as LBA and NORMAL. What do these modes mean? Current motherboards support three hard disk working modes: NORMAL, LBA, and LARGE mode.
NORMAL mode is the earliest IDE method. In this mode, when accessing the hard disk, the BIOS and IDE controller do not perform any parameter conversion. The maximum number of cylinders supported by this mode is 1024, the maximum number of heads is 16, the maximum number of sectors is 63, and the number of bytes per sector is 512Byte. Therefore the maximum hard disk capacity supported is: 12×63×16×1024=528MB. In this mode, even if the actual physical capacity of the hard disk is larger, the accessible hard disk space can only be 528MB.
LBA (Logical Block Addressing) mode. The hard disk space managed by this mode breaks through the 528MB bottleneck and can reach 8.4GB. Under LBA mode, the set parameters such as cylinders, heads, and sectors are not the actual physical parameters of the hard disk. When accessing the hard disk, the IDE controller converts the logical address determined by parameters such as cylinders, heads, and sectors into the actual physical address of the hard disk. Under LBA mode, the maximum number of heads that can be set is 255, and the remaining parameters are the same as in NORMAL mode. From this it can be calculated that the accessible hard disk capacity is: 512×63×255×1024=8.4GB.
LARGE mode. When the hard disk has more than 1024 cylinders and is not supported by LBA, this mode can be used. The method used by LARGE mode is to divide the number of cylinders by 2 and multiply the number of heads by 2, so that the total capacity remains unchanged. For example, under NORMAL mode the number of cylinders is 1024 and the number of heads is 16; after entering LARGE mode, the number of cylinders becomes 610 and the number of heads becomes 32. In this way, as far as DOS is concerned the number of cylinders is less than 1024, so it can work normally. At present, basically only LBA still has practical meaning.
NORMAL mode is the earliest IDE method. In this mode, when accessing the hard disk, the BIOS and IDE controller do not perform any parameter conversion. The maximum number of cylinders supported by this mode is 1024, the maximum number of heads is 16, the maximum number of sectors is 63, and the number of bytes per sector is 512Byte. Therefore the maximum hard disk capacity supported is: 12×63×16×1024=528MB. In this mode, even if the actual physical capacity of the hard disk is larger, the accessible hard disk space can only be 528MB.
LBA (Logical Block Addressing) mode. The hard disk space managed by this mode breaks through the 528MB bottleneck and can reach 8.4GB. Under LBA mode, the set parameters such as cylinders, heads, and sectors are not the actual physical parameters of the hard disk. When accessing the hard disk, the IDE controller converts the logical address determined by parameters such as cylinders, heads, and sectors into the actual physical address of the hard disk. Under LBA mode, the maximum number of heads that can be set is 255, and the remaining parameters are the same as in NORMAL mode. From this it can be calculated that the accessible hard disk capacity is: 512×63×255×1024=8.4GB.
LARGE mode. When the hard disk has more than 1024 cylinders and is not supported by LBA, this mode can be used. The method used by LARGE mode is to divide the number of cylinders by 2 and multiply the number of heads by 2, so that the total capacity remains unchanged. For example, under NORMAL mode the number of cylinders is 1024 and the number of heads is 16; after entering LARGE mode, the number of cylinders becomes 610 and the number of heads becomes 32. In this way, as far as DOS is concerned the number of cylinders is less than 1024, so it can work normally. At present, basically only LBA still has practical meaning.
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