Heya,
I am little confused about the following issues, which i would appreciate your help.
1- Can the user through a CPU instruction change directly the CPU mode bit and the PWS content? Or does he have to call INT so the mode bit is set to 1 and RETE to reset it back to 02- i can't see why the user mode kernel mode concept is still nowadays maintained. i understand that with user mode, user applications have some restrictions. they can't access the computer system devices directly, while with mode bit set to kernel or supervisor mode, the whole system components can be altered. I understand that for security reasons, accessing memory and IO devices has to be done by a code (kernel code, driver code) which has been thouroughly tested and carefully and efficiently written. however, why a need to switch the CPU mode bit??? there is enough hardware support to ensure that no process can access unauthorised memory region of an other (user/kernel) process. so presumably this mode bit setting has not been maintained to protect processes from each other as dedicated hardware is there to trap the OS in case of unauthorised access but rather maintained for another reason ..... any help with example please???
Thanks