Messages in this thread | | | Date | Wed, 15 Feb 2006 15:54:24 -0500 | From | Phillip Susi <> | Subject | Re: RFC: disk geometry via sysfs |
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linux-os (Dick Johnson) wrote: > If the disc is a modern disk, and the BIOS is modern as well, > it won't care. For instance, if we attempt to seek to cylinder > 10, sector 10, and there are only 9 sectors, then the supplied > head number is incremented, the sector to be read becomes 1 > (dumb ones based), and everything is fine. If the head number > can't be incremented, it wraps to 0. Problems occur if the BIOS > has been set to "physical" mode for access. In this mode, the > CHS are absolute and "you can't get there from here." In the > physical mode, you can't have more than 1024 cylinders because > they need to fit into 10 bits. > > As long as the BIOS is set for LBA, the boot sequence should not > care. >
Are you sure? Do all bioses perform this auto correction? I would have thought that they would simply fail the request because you asked for a sector or head that is outside the valid range. Even if some bioses will accept illegal values and auto translate, I doubt that they all do.
And what if you error in the other direction? If the MBR lists a LOWER number of heads than the bios thinks there is? In that case you're going to ask the bios for a larger cylinder number, and it will happily read a sector from the disk that is further from the start than you intended.
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