Hi Khader,
>And can anybody elaborate why Unix uses only two levels and
>why not all the four ?? And anybody here knows what are the four levels in
>the Intel
>processors.
Actually UNIX uses two levels in hardware and simulates the other levels
through software. One reason for not using all the four modes is that
flexibility is lost. I will explain this further:
When we talk of levels, we are actually talking about the level of
protection in a particular level. At the highest level you have all the
rights to change any of the CPU registers. At the lowest level you have
rights just enough to perform your work.
Here we can implement more levels as done by Intel, by gradually
increasing the protection from the lowest to the highest level.
This is theoretically a good idea, but when it comes to practical
implementation, this reduces the flexibility. As you are aware, the
superuser (root) has the flexibility of granting a particular right to a
particular (or a group of) users. This would require several level changes
for those users. This further makes the implementation of the OS quite
complicated.
Regarding the four levels, I think they are just named from level 0 to
level 3 (level 0 being the highest protection).
Note: I may not be right at this one, others please correct ?
Regards
Nitin
>Thanks
>Regards
> Khader
>
>---------------------------------- @}--------
>Syed Khader Vali Debian 2.2.1 ( potato )
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