Simply that is easier to provide segments that are not fit to be
reloaded before the kernel sets up it's own GDT. Then to ensure you
stick a GDT someplace that won't get stomped.
Especially before we froze which segments numbers the kernel
would load into the boot protocol. I would have used this in
places where I was doing 32bit bootloader work as it is just easier to
support.
Eric
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