Hidden spot on hard drives?

Jerry McAllister jerrymc at clunix.cl.msu.edu
Thu Oct 6 10:03:02 PDT 2005

> Norberto Meijome <freebsd at meijome.net> writes:
> > Where does HPA(Host protected Area) sit in all this? is this the
> > 'boot sector' trick?
> I don't know.  I just heard that some computer makers are somehow
> reserving as much as half the HDD for a full copy of the OS to recover
> from when the normal one trips over itself.  I'm guessing that this has
> more to do with MSFT licensing terms than with saving a buck from not
> including a CDROM.  I wonder if there's some low-level way to tell a
> modern disk drive where you want "sector 0" to start.

Manufacturers put all sorts of stuff in areas on the disk that 
will not normally show up if you are booting an MS system.  But those
areas are just disk outside the current slice to FreeBSD.  An example
is Dell makes a bootable diagnostic section on its disks.   It will
only normally boot when you choose run diagnostics during boot.  But
if you create a "dual" booted machine with FreeBSD, then to FreeBSD it 
is just slice 1, XP is slice 2 and FreeBSd is slice 3.  The FreeBSD MBR
recognizes it and lists 1 - ???,  2 - DOS,  3 - FreeBSD at boot time.
If the "reserved" slice was not bootable, I don't think it would
mention it in the boot menu, but it would still be just plain disk
in another slice to FreeBSD.     

As others have mentioned, some have tried to make special drivers
that do funny things like half-stepping the heads or accessing
the replacement sector area.   But, the same type of software could
be written to access it and if FreeBSD were installed, it would ignore
that stuff unless some driver was created and installed to access it.
So, it wouldn't make much of a protection scheme.

As for moving sector 0, I don't know.  It would probably have to
be something in the controller, but???


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