WGU C191 Home Study Thorough Review and Complete Answers Ace your first Attempt Updated 2024/2025
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WGU C191
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WGU C191
WGU C191 Home Study Thorough Review and Complete Answers Ace your first Attempt Updated 2024/2025
Interrupt - correct answer A hardware signal indicating that the hardware needs servicing (or attention).
Blocking: I/O - correct answer When an application issues a blocking system call, the exe...
WGU C191 Home Study Thorough Review
and Complete Answers Ace your first
Attempt Updated 2024/2025
Interrupt - correct answer A hardware signal indicating that the hardware needs
servicing (or attention).
Blocking: I/O - correct answer When an application issues a blocking system call, the
execution of the application is suspended. The application is moved from the operating
system's run queue to a wait queue. After the system call completes, the application is
moved back to the run queue. When it resumes execution, it will receive the values
returned by the system call. It is used for the application interface.
Nonblocking I/O - correct answer a user interface that receives keyboard and mouse
input while processing and displaying data on the screen. This is used for I/O devices.
Synchronous vs asynchronous I/O - correct answer different names for blocking and
nonblocking I/O. The thing to remember is that async and nonblocking I/O returns
results immediately unblocked while waiting for a process to complete its execution
Memory-mapped I/O - correct answer I/O controller talking to main memory directly
without CPU interrupt before the operation is completed. Interrupt is only sent after
operation completion.
FCFS: First Come and First Served - correct answer Non-preemptive
Not good for time-sharing systems
Round Robin scheduling: - correct answer Preemptive
Add a timer, move the running thread to the back of the queue after each time slice
Priority scheduling: - correct answer Preemptive or non-preemptive
,Equal-priority processes are scheduled in FCFS order
Starvation is a problem but aging is a solution (i.e., increase priority as time goes by)
Shortest Job First (SJF/SRTF) - correct answer Preemptive or non-preemptive
A special case of priority scheduling
Preemptive SJF is called shortest remaining time first (SRTF) - shorter CPU burst of
upcoming process can preempt running processes
I/O bound jobs get priority over CPU bound jobs
Multilevel queue - correct answer Processes are classified into different groups
Multiple queues with different fixed priorities (system, interactive, interactive editing,
batch, student)
Processes are permanently assigned to one queue (can't be reassigned)
Multilevel feedback queue - correct answer Multiple queues with different flexible
priorities (system, interactive, interactive editing, batch, student)
Use round robin scheduling at each priority level, running jobs in highest priority queue
first
Use past behavior to predict the future and assign job priorities
Feedback queues can have different scheduling algorithms at different levels
Threads vs Processes: - correct answer both processes and threads are independent
sequences of execution. Threads (of the same process) run in a shared memory space,
while processes run in separate memory spaces.
Threads are bound to a single process
Address space of a process is shared among all its threads.
No system calls are required to communication between threads - simpler than inter-
process communication (IPC).
Switching between threads is faster than context switching.
, Two types of threads - correct answer user threads and kernel threads.
Pthreads - correct answer refers to the POSIX standard (IEEE 1003.1c) defining an
API for thread creation and synchronization.
Swapped - correct answer processes (swapped out by a dispatcher) need to be
swapped into the same memory space it occupied previously from a backing store (a
temporary memory location usually a hard disk), but it depends on the address binding
method (load time address binding - the same memory space, execution time address
binding - different memory space).
Virtual memory - correct answer a storage scheme where secondary memory can be
treated as though it is a part of main memory. Only part of the process that is actually
needed will be loaded into actual main memory while part of code that is rarely used
can be loaded into the virtual memory.
Demand Paging - correct answer Pages are only loaded when they are demanded
during program execution.
Use a lazy swapper (swap only it is needed) to swap a page into the memory.
Pages in memory vs Pages on disk?
Make use of present/absent bit or valid/invalid bit
When it is invalid, it's called a page fault
Copy on write: - correct answer a technique that is used for sharing virtual memory or
pages. Used in conjunction with fork() system call to create child processes.
copy on write - correct answer fork() will create a copy of the parent's address space
and memory pages.
We can optimize by making the parents and child share common pages (pages that
can't be modified such as containing executable code) and only create a copy of page
when either one wants to modify/write a page. - this is called copy on write
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