A Protected Kernel

0

2n

code library

OS data

OS code

Program A

data

Data

Program B

Data

registers

CPU

R0

Rn

PC

main memory

x

x

mode

CPU mode (a field in some status register) indicates whether the CPU is running in a user program or in the protected kernel.

Some instructions or data accesses are only legal when the CPU is executing in kernel mode.

physical address space

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