which of the following is correct,please explain every point

Question

A multiuser multi-programming O.S can't be implemented on hardware that doesn't support,

. address translation

.DMA for disk transfer

.at least two modes of cpu execution(privileged and non-priviliged)

.demand paging

Answer 1

Ans : <c>.at least two modes of cpu execution(privileged and non-priviliged)

Explaination :

a) We can make a system multi user and multi-programming even by not using Virtual memory. We can use static partitions in Main memory to do our job. It's just that the degree of multi-programming will be less. But it is possible.

b) DMA has nothing to do with multi programming if we consider only processes to be CPU bound.

d) demand paging, Reason same as option a. Without VM we can make a system to ne multi programmed.

Why option c?

Because in case of multiuser system, one user will be root user for sure which will have access to privilaged instructions.

So to switch from normal user to root user you need hardware bit which is switched between two modes of uses. Also for a system to be multi programming, we need to swap in and out the processes from memory which need hardware access which can be only done in system mode.

Comments

Consider a virtual machine installed on a system. Now inside it we have root, normal users. Do we nee hardware support here?

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This is an intersting scenario. Note that a virtual machine simulates the whole environment virtually for a OS to run on it. So it simulates all those features.
 

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Yes. That's it- OS can simulate. But address translation cannot be done like that. Static partitioning won't work in real scenario. Because we need to partition for per user and per process. So, it will be like about 5 users can use the system and each one of them can run 5 processes- not possible in real environment where we need like 100s of processes per user and sometimes a single user needs like 90-100% of total memory.