5 Oct
2007
5 Oct
'07
7:10 a.m.
tuhs(a)cuzuco.com wrote:
8086 lacks the required protected mode. don't
remember how xenix over
came this problem when it was first released. no one even has to think
about this problem today
Xenix for the 8086 only supported "small model" user programs of up to
64k text + 64k data
and used the segment registers to point to the appropriate text and data
segments in physical
memory. User programs were not supposed to ever look at or change the
contents of their
segment registers - if they did then chaos was likely to ensue.
And, of course, there was no protection so a rogue process could access
all of physical
memory including the memory used by the kernel.
It's quite amazing that it worked as well as it did.
md