(1.5) How does the distinction between kernel mode and user mode function as a r

Question

(1.5) How does the distinction between kernel mode and user mode function as a rudimentary form of protection (security) system? (1.10) Give two reasons why caches are useful. What problems do they solve? What problems do they cause? Ifa cache can be made as large as the device for which it is caching (for instance, a cache as large as a disk), why not make it that large and eliminate the device? (1.11) Distinguish between the client-server and peer-o- peer models of distributed systems. (L 1 5) Describe the differences between symmetric and asymmetric multiprocessing. What are three advantages and one disadvantage of multiprocessor systems? (1.27) Describe some of the challenges of designing operating systems for mobile devices compared with designing operating systems for traditional PCs (1.30) Identify several advantages and several disadvantages of open-source operating systems. Include the types of people who would find each aspect to be an advantage or a disadvantage.

Explanation / Answer

1.5

Kernel mode has the most trusted operating system functions that have unrestricted and open access to any underlying hardware or address space of the system. It can execute any kind of CPU instructions. If there is any crash in the kernel mode then the system experiences a complete halt.

Crashes in User mode is recoverable because codes that are run under this mode are not allowed to access hardware or any address space directly. To access hardware it needs to ask system API's for permission. If a code running under user mode wants to access some restricted hardware instruction

the particular application crashes.

1.10.

Cache memory is a virtual memory. Generally the informations which are frequently needed are stored in the cache to find it in a lesser time than finding it throughout the whole disk area.

It also helps to set up right connection between the components wanting to transfer some data but they have different clock speed. Cache provides the right kind of buffer medium to transfer data smoothly.

Actually what it does is, it supplies the right kind of data on behalf of the slower device , that is needed by the faster device from the slower device. Beacuse it has recently used datas stored in it. Data is updated within the cache using replacement policies.

1.11.

Client -Server Peer to Peer

1) Client-Server model has specific server 1) Any node can act both as a

and specific clients associated with the server.   client and server. Any node can

So any client would request server for any server. ask for any service and provide service.

2)Here centralized server stores data and the 2) As all the nodes or peers

model shares informations. have their own data they focus on connectivity more.

3)Here the request comes to only one 3) As all the nodes can provide

node , so for a lot of requests it can turn service so no bottleneck

into a bottle neck. possible.

4) In this model implementation is really 4) Though it is less costly but if

costly and stable. number of peers increase it

will be unstable.

5) Less privacy as it is possible to see who is 5) More privacy than client server

inserting data. model.

1.15

Symmetric Asymmetric

1)Here several processors have common 1)Several processors have their

OS and memory. OS and memory.

2)Processors takes processes from a ready 2) Either have predefined

queue which is common or they even may   processes or master allocates

have one ready queue for each processor. processes to the slaves.

3) Synchronisation of processors needed to 3) It is very simple because master

maintain load balance. process can access the whole

data structure.

4) uses multiple CPU of same architecture is 4) Multiple CPU with different

used.   architecture is used.

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