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Why does an OS have a kernel
- Fair resource allocation
an instance of a program, running with limited rights
a sequence of instructions within a process
Prevent buggy program from causing crashes
Limit the scope of what untrusted programs can do
On a multiple-user OS, each user must be limited to only data that the user is permitted to access
OS limit the amount of resource allocated to each app
Fair resource allocation
set of rights of a process Memory that the process can access
set of rights of a process
How can we implement execution with limitedprivilege?
- Execute each program instruction in a simulator
- – If the instruction is permitted, do the instruction
- – Otherwise, stop the process
The operating system keeps track of the various processes on the computerusing a data structure
process control block
How do we go faster?
Run the unprivileged code directly on the CPU!
the processor checks each instruction before executing it to verify that it is permitted to be performed operation by that process
theoperating system executes with protection checks turned off
In kernel mode
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