Re: [LI] user space, kernel space and .........

["nitin gupta" <n_k_gupta20@xxxxxxxxxxx>]

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 )
> skhader@xxxxxxxxxx             Kernel 2.3.39
> Live Free or Die                       http://www.cfp2000.org
>
>
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