Explain Address Translation In Operating System, Dual Mode Operation
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Address Translation
• Address Space– A group of memory addresses usable by something
– Each program (process) and kernel has potentially
different address spaces.
• Address Translation:
– Translate from Virtual Addresses (emitted by CPU)
into Physical Addresses (of memory)
– Mapping often performed in Hardware by Memory
Management Unit (MMU)
Translation helps protection:
– Control translations, control access
– Should Users be able to change Page Table???
Dual Mode Operation
• Hardware provides at least two modes:– “Kernel” mode (or “supervisor” or “protected”)
– “User” mode: Normal programs executed
• Some instructions/ops prohibited in user mode:
– Example: cannot modify page tables in user mode
• Attempt to modify Exception generated
• Transitions from user mode to kernel mode:
– System Calls, Interrupts, Other exceptions