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COP4610 - Final Exam with 100% correct answers
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COP4610 - Final Exam with 100% correct answers
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COP4610 - Final ExamDescribe two general roles of an OS, elaborate why these roles are important. - correct answer
✔✔Provide an abstraction layer for software to run on machine, w/o knowing hardware
implementations.
IMPORTANT:
- Reduces burden on developers.
- Extends hardware w/ added functionality.
- Provides a common base for all applications.
Provide resource management to users by ensuring progress, fairness, and efficient usage of computing
resources.
Name three ways in which the processor can transition from user mode to kernel mode?
Can the user execute arbitrary code after transition? - correct answer ✔✔Trap (system calls)
Interrupt (I / O)
Exception (divide by 0)
Can the user execute arbitrary code after transition? - correct answer ✔✔No, users, can't execute
arbitrary code b/c entry to kernel mode contains a set of restricted routines that ensures only the kernel
is running an not the users.
What is a mutex? - correct answer ✔✔It's a lock, a program object that allows multiple program threads
to share the same resource.
What is a semaphore? - correct answer ✔✔A synchronization tool used to solve complex critical section
problems.
, What is the difference between a mutex and a semaphore? - correct answer ✔✔For mutex, only it's
threads that locked or acquired the mutex can unlock it.
Whereas semaphore, a thread waiting on a semaphore can be signaled by a different thread.
What is context switch? - correct answer ✔✔Is transferring control from one process to another process.
Requires saving the state of old process and loading the saved state for the new process.
Why is switching threads less costly than switching processes? - correct answer ✔✔Less state needs to
be saved and restored when switching threads rather than process;
Switching between threads benefits from cache whereas switching between processes invalidates the
cache and TLB that caches the page table.
Describe how OS deals with a page fault?
You should consider using a workflow map in your answer. - correct answer ✔✔Start from CPU (vpn) ->
Look up TLB (miss) ->
PT Look up (miss and locate) ->
File (i/o) ->
Pg frame (vpn, pfn) ->
PT update (vpn, pfn) ->
TLB update -> PF service compete.
What's TLB? - correct answer ✔✔Translation look-aside buffer.
What's TLB used for? - correct answer ✔✔Memory cache used to reduce the time taken to access a user
memory location.
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