Comp111 - Operating Systems
Quiz 2 - Nov 25, 2013 - closed book
Closed book and notes. No electronic devices allowed.
Please fill in the blanks. Each blank is worth 5 points.
Blanks with the same number have the same answer.
- If 20 people per hour arrive at a restaurant, and the same number
of people leave every hour on average, and we observe that people stay
an average of 2 hours, then there are ____40____
people on average inside the restaurant. This is only true because
the system is in ____balance/steady state____ and because all values
are ____averages____. If -- in addition -- there are
always an average of 5 people waiting in line to be seated inside the
restaurant , then the wait for seating is an average of
For (1), λ=20/hour, W=2 hours, and the number of people in
the restaurant is L=λW = 40. For (4), λ=20/hour and
L=5, so W=L/λ=5/20 = 1/4 hour.
- Inside an operating system, names are for human use and most
entities are identified by ____numbers____; thus it is
convenient to store many kinds of internal entity descriptors in
- A scheduler is called ____fair____ if every process in
the run queue receives the same amount of time. In O(1) scheduling,
every process gets one time slice per ____epoch____.
This is not considered
____fair____ because it does not compensate for time a
process spends ____waiting/sleeping____ for other events.
The ____completely fair____ scheduler gives such processes extra time.
- The buddy system guarantees that if one frees and then
reallocates the same amount of storage, one will always get the
____same____ memory back. This is because the freed
block is linked at the ____head/beginning____ of the
appropriate free list.
- If several processes have the same file open, they all share the
same ____kernel____ descriptor for the file. If every
process used a different one to write to the same file, then output
could potentially be ____lost/overwritten____.
- From the point of view of a process, memory fragmentation of the
frame table is called ____external____ fragmentation,
while fragmentation due to malloc is called
____internal____ fragmentation. From the operating
system's point of view, fragmentation of the frame table is
- Modern memory addressing uses ____hashing____ to
represent sparse maps, and ____caching____ to represent
dense maps. Segments are utilized to decrease the amount of
information one must store about each memory
- (Extra credit) Determining whether to execute a process
is called ____admission____ control.