Comp111 - Quiz 2 Review 3 answers
Dec 8, 2009 - closed book
Please fill in the blanks. Each blank is worth 5 points.
There are several reasonable answers for some of the blanks; choose one.
Blanks with the same number have the same answer.
Extra credit answers count only if errors are made in the regular quiz;
in no case will one's score be greater than 100.
Each page in a memory page table has attributes known to the operating
system but not necessarily known to the processes that utilize the page.
These attributes include whether the page is
____read-only/readable/writeable/etc (I think I should also accept available; if you put this there, then have me regrade it)____ to a process, as well as whether it
____shared/associated____ with other processes.
These attributes take up a significant amount of space in memory,
so that some operating systems define them by specifying them for each
____segment (alas, process is incorrect)____ rather than for each page.
- An inverted page map differs from a regular page map because
each page address is
____hashed____ into an offset
into the page table rather than being interpreted as an offset into
the page table. This means that one can often hop directly to
the appropriate page map
entry, but sometimes one must
____search/scan/skip____ within the
page table for an appropriate entry.
Each entry of an inverted page map must thus contain the real offset
of the page, as well as an identifier of the
____process____ that owns the page.
Without this extra information, the mapper can't tell the difference between
pages intended for use by different
- The inter-arrival time and service time distributions actually have the same
____cumulative/probability (I think I should also accept "exponential")____ distribution function
but describe different things. The
inter-arrival time distribution describes
successive events, while the service time distribution describes time
required to ____service/process____ a particular event.
If λ represents the rate of arrival of events, and μ represents
the rate of processing, then λ/μ represents the
that the associated queue of events contains 0 elements,
while (λ/μ)n(1-(λ/μ)) represents the
____probability____ that the queue contains exactly n elements.
This is only true if the queueing system achieves steady-state behavior, i.e.,
λ/μ < ____1.0____.
If it achieves steady-state behavior, the balance equations say that
the input and output
for each particular queue are the same, while the
____service times/mean time in system____ for each queue may differ greatly from
that of other queues.
- In paging systems, the translation lookaside buffer serves as a
____cache/in-memory representation____ of the translations between
and physical page addresses.
As it is limited in size, its contents are sometimes treated as
memory, and paged in and out just like process pages.
In assignment three, the deadlock detection algorithm often detects
deadlock conditions that do not persist. This is because the deadlock
is caused by choices made by the
rather than choices made by the processes.
Unlike individual processes, the pager has a
view of resource needs over all processes.
This means that it can
potential deadlock conditions when they occur, simply by making
more informed choices.
- (EXTRA CREDIT: can increase score to 100, but not above 100)
A virtual memory paging system may be modelled as an M/M/c queueing system,
where 1/λ is the average time between page
1/μ represents the average time it takes to
____swap/load____ a page into physical memory, and
c represents the number of
____swap/load____ operations that can occur concurrently.
Increasing the amount of physical memory
____decreases____ λ; this is strongly recommended