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Probably not, since any protection scheme devised by a human can also be broken and the more complex the scheme is, the more difficult it is to be confident of its correct implementation. As compared to dedicated machines, time-shared machines are far less secure, and are very easy to overload the buffers. They are also much slower to catch a virus. But in dedicated machine, all resources are available to the process being run.
Q2) Under what circumstances would a user be better off using a time sharing system rather than a PC or single user workstation?
Ans . When there are few other users, the task is large, and the hardware is fast, time-sharing makes sense. The full power of the system can be brought to bear on the user’s problem. The problem can be solved faster than on a personal computer. Another case occurs when lots of other users need resources at the same time. A personal computer is best when the job is small enough to be executed reasonably on it and when performance is sufficient to execute the program to the user’s satisfaction.
Q3) In the designing of the operating system there are two approaches modular kernel and layered approach? How are they different?
Ans. There are various differences between moduler kernel and layered approach:-
A modular kernel differs from a layered approach in that there is less overhead in making a call to a lower level part of the kernel. The call doesn’t have to jump through numerous layers before work gets done and parts are aware of any other parts of the kernel and not just what is below them.
Modular kernel is more secure as compared to layered approach, as more operations are done in user mode than in kernel mode.
Debugging and modification of data is much easier in layered approach because changes affect only limited sections of the system rather than touching all sections of the system.
In modular kernel approach, kernel design and its functionality are more simple as compared to layered approach.
Q4) There is guest operating system and a host operating system like VMware? List all the factors in choosing the host operating system?
Ans. A host operating system is the operating system that is in direct communication with the hardware. It has direct hardware access to kernel mode and all of the devices on the physical machine. The guest operating system runs on top of a virtualization layer and all of the physical devices are virtualized. A host operating system should be as modular and thin as possible to allow the virtualization of the hardware to be as close to the physical hardware as possible, and so that dependencies that exist in the host operating don’t restrict operation in the guest operating system.
Q5) The kernel is responsible for a action with the processes. Search through the action of kernel and describe what is the action?
Ans. The various actions of the kernel are as follows:
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The main task of a kernel is to allow the execution of applications and support them with features such as hardware abstractions.
To run an application, a kernel typically sets up an address space for the application, loads the file containing the application’s code into memory, sets up a stack for the program and branches to a given location inside the program, thus starting its execution.
The kernel uses scheduling algorithms to determine which process is running next and how much time it will be given. The algorithm chosen may allow for some processes to have higher priority than others.
To perform useful functions, processes need access to the peripherals connected to the computer, which are controlled by the kernel through device drivers.
If sometimes the interrupt has been occurred during execution of any process then it saves the state(address) of current process, and after that when interrupt has been removed then it restores the state(address) of previous process.
Q6) Considering both the system level and the programmer level.
Consider the advantage and disadvantage of the following structure.
Synchronous and asynchronous communication.
Automatic and explicit buffering.
Send by copy and send by reference
Fixed-sized and variable-sized message.
Synchronous and asynchronous communication-
Advantage: you can get an immediate response; instant feedback fosters communication; there seems to be a more emotional bonding effect between people when there is a possiblity to communicate in real time (synchronously), spontaneity.
Disadvantage: There is less time to think about what you want to say or your response to another; time may be a limiting factor, e.g time zones; synchronous communication over the computer may be difficult because of the speed of data transaction with slower connections; you need extra equipment (speakers, microphone, webcamera).
Advantage: you have time to think about what you want to say; time is not a constraint. You can receive the message whenever you have time and you can analyze the content of the message more carefully so the answer you give can be even more meaningful because it has gone through a process of elaboration.
Disadvantage: no immediate response, especially where time is significant; you may not know if the other person has received your message; the message loses human contact
Automatic and explicit buffering –
Automatic buffering :
Advantage: Automatic buffering provides a queue with inde¬nite length ; thus ensuring the sender will never have to block while waiting to copy a message.
Disadvantage: There are no specifications how automatic buffering will be provided; one scheme may reserve sufficiently large memory where much of the memory is wasted.
Advantage: Explicit buffering speci¬es how large the bufferis.
Disadvantage: In this situation, the sender may be blocked while waiting for available space in the queue. However, it is less likely memory will be wasted with explicit buffering.
Send by copy and send by reference –
Send by copy:
Advantage: send by copy is better for synchronization issues.
Disadvantage: Send by copy does not allow the receiver to alter the state of parameter.
send by reference:
Advantage: A bene¬t of send by reference is that it allows the programmer to write a distributed version of a centralized application Java’s RMI provides both, however passing a parameter by reference requires declaring the parameter as a remote object as well. Send by reference also allow the receiver to alter the state of parameter.
Disadvantage: send by reference can compromise the security of an organisation because sensitive information can be easily distributed accidently or deliberately.
Fixed-sized and variable-sized messages –
Advantage: The implications of this are mostly related to buffering issues; with ¬xed-size messages, a buffer with a speci¬c size can hold a known number of messages.
Disadvantage: with ¬xed-sized messages the messages are copied from the address space of the sender to the address space of the receiving process.
Advantage: variable-sized messages (i.e. Larger messages) use shared memory to pass the message.
Disadvantage: The number of variable-sized messages that can be held by such a buffer is unknown.
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