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1. [20 points, 1 each] true or false, circle t or f.

a. A binary semaphore takes on numerical values 0 and 1 only.

b. An atomic operation is a machine instruction or a sequence of instructions

that must be executed to completion without interruption.

c. Deadlock is a situation in which two or more processes (or threads) are waiting for an event that will occur in the future

d. Starvation is a situation in which a process is denied access to a resource

because of the competitive activity of other, possibly unrelated, processes.

e. While a process is blocked on a semaphore's queue, it is engaged in busy waiting.

f. Circular waiting is a necessary condition for deadlock, but not a sufficient

condition a condition for the deadlock to occur.

g. Mutual exclusion can be enforced with a general semaphore whose initial value is greater than 1

h. External fragmentation can occur in a paged virtual memory system.

i. External fragmentation can be prevented (almost completely) by frequent use of compaction, but the cost would be too high for most systems.

j. A page frame is a portion of main memory.

k. Once a virtual memory page is locked into main memory, it cannot be written to the disk.

l. Pages that are shared between two or more processes can never be swapped out to the disk.

m. The allocated portions of memory using a buddy system are all the same size.

n. Demand paging requires the programmer to take specific action to force the

operating system to load a particular virtual memory page.

o. Prepaging is one possibility for the fetch policy in a virtual memory system.

p. The resident set of a process can be changed in response to actions by other processes.

q. The working set of a process can be changed in response to actions by other processes.

r. The translation lookaside buffer is a software data structure that supports he virtual memory address translation operation.

s. In a symmetric multiprocessor, threads can always be run on any processor.

t. Thrashing will never be a problem if the system has 1 GB of real memory.

2. [20 points, 5 each] short answers and simple diagrams.

(a) Define the resident set of a process.

(b) Define the working set of a process.

(c) What problems could occur if virtual memory pages are always allocated in groups of four?

(d) What information is used by the Least Recently Used page replacement policy, and how does this compare to the information used by the various Clock algorithms?

3. [20 points, 5 each] short answers and simple diagrams.

(a) In terms of memory allocation, what is a reference counter? Why is it needed?

(b) Explain why, or why not, internal fragmentation can be a problem when using the best fit algorithm for memory allocation.

(c) One of the options in a mainframe OS is to limit the number of jobs (processes) currently in the system. What are some of the benefits of this capability?

(d) In what circumstances of virtual memory is the placement policy an important issue?

4. [20 points, 5 each] short answers.

(a) What are four general characteristics of processor scheduling policies?

(b) Define Turnaround Time and Normalized Turnaround Time. Why are these useful for measuring the performance of a scheduling algorithm?

(c) What would be the effect of a large number of page faults by a process on that process's page allocation on a nonpreemptive operating system?

(d) What are four actions or decisions that a preemptive virtual memory operating system would make at the end of a time quantum (in response to a timer interrupt)?

5. [20 points]

This function is proposed for use in an operating system, with the definitions of

Process, Process_Set and other functions given elsewhere.

Process next_process(Process_Set available_processes) {

Process_Set A = highest_valuation(available_processes); /* priority ranking */

Process_Set B = earliest(A); /* actual arrival time */

Process c = random_selection(B); /* tie-breaker */

return c; /* run this process next */

}

(a) [5] Explain why this function could lead to processor starvation among the available processes.

(b) [5] Suppose one of the criteria used by the highest_valuation function is the process's fraction of virtual memory pages currently in main memory. Explain why this is not a good idea.

(c) [10] Define a version of the highest_valuation function (in the same style, but with some more descriptive comments) for the Shortest Process Next scheduling policy. Describe the data requirements and how this data is obtained.

Questions & Answers

Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
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Source:  OpenStax, Operating systems. OpenStax CNX. Aug 13, 2009 Download for free at http://cnx.org/content/col10785/1.2
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