Dual mode operation

Dual-mode operation makes a trade-off between a user mode and kernel mode when executing programs.

There are distinct execution modes supported directly in hardware: - In kernel mode, a process has full privilege with the hardware - In user mode, a process has limited privilege on the hardware

What dual-mode operation provides for the hardware: - Privileged instructions - Exception handler: will talk to kernel if a process has gone bad - memory protection - Timer interrupts - Mode switch