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The operating system and the other processes are protected from being modified by an already running process because

1. they run at different time instants and not in parallel
2. they are in different logical addresses
3. they use a protection algorithm in the scheduler
4. every address generated by the CPU is being checked against the relocation and limit parameters

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The Operating System uses two registers to implement memory protection, namely relocation register and limit register. Together, they can define the range of addresses a process can validly refer to.

When the dispatcher dispatches a process from ready to running state, the relocation register and the limit registers are given the respective values as per that process.

Each logical address generated by the CPU is checked against these registers to figure out if the logical address is out of bounds for the given process. This is how memory protection is implemented.

Option D

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Option D).

Relocation and limit registers checks the address request made by process and prevents the system from accessing memory of other program.

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Here in the question, they have asked about "because" and not "how" so isn't option b) more appropriate?
yes I also think so.
Option B is one of the factors of option D.
Let's see what comes in the official key.

We always have to go for the most appropriate answer. Technically Option C is also correct. But Option D states the precise reason. Don't get drawn too much into semantics, bro.

D is correct.

Every address generated by the CPU is being checked against the relocation and limit parameters to ensure security.

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option D as the logical address generated by CPU is being checked by the Relocation Register (base register which contain the smallest PHYSICAL ADDRESS and Limit register which contain the range of the LOGICAL ADDRESS and one process can not modify other processes or operating system.
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