Messages in this thread | | | Date | Sun, 30 Nov 2003 13:58:34 GMT | From | John Bradford <> | Subject | Re: Disk Geometries reported incorrectly on 2.6.0-testX |
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Quote from Andries Brouwer <aebr@win.tue.nl>: > On Sun, Nov 30, 2003 at 03:22:52AM +0100, Andrzej Krzysztofowicz wrote: > > > > The BIOS reads the MBR and jumps to the code loaded from there. > > > There is no need for any partition table, or, if there is a table, > > > for any particular format. It is all up to the code that is found > > > in the MBR. > > > > I found some PC BIOS-es refuse to read the MBR if no active partition is > > found in the partition table... > > Yes. We are getting a bit away from disk geometries, but it is true > that there are many broken BIOSes that in some way depend on partition > table format or MBR format.
OK, there is broken hardware, but there are also people with non-broken hardware who want to make better use of it :-). I am not recommending that everybody moves away from the standard partition table format, I just want a better partitioning scheme for new machines I build, (for which I would avoid using known broken hardware).
> I recall the report that one BIOS tuned IDE modes by reading the MBR > and seeing whether it ended with 0xaa55. If not it tried a lower speed. > So on a disk without this MBR signature, the I/O would be slow. > > BSD used to use an entirely different partition table scheme. > And it was not uncommon to run a whole-disk BSD system, without > any partitioning.
Hmmm, yes, you can use a BSD disk label on a whole disk, as opposed to putting a BSD disk label on one partition of a disk. I have never tried to read such a disk on a Linux machine, though - do we support that correctly?
> Increasingly often that caused problems with broken BIOSes > that wanted to interpret partition table contents. > > The categories of problems that come to mind are: > - BIOS has a virus detection option and checks the MBR > - BIOS inspects the partition table to find the hibernation partition > - BIOS inspects the partition table to find the service partition > - BIOS inspects the partition table to guess what geometry it should report > > I recall that certain Thinkpads would not boot FreeBSD even with a DOS-type > partition table because the BIOS did not like the a5 partition ID. > > So, yes, you are right, practice is much more complicated than theory.
For building new, dedicated Linux machines, though, how much of that do we have to concern ourselves with?
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