[TUHS] New V7 port available

Michael Davidson MichaelDavidson at pacbell.net
Fri Oct 5 15:10:38 AEST 2007

tuhs at 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.


More information about the TUHS mailing list