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What is thrashing and how can an operating system take steps to avoid it?

 

      Thrashing occurs when a system spends more time swapping than running a process. The operating system can avoid thrashing by reducing the number of processes that are in memory, i.e. by swapping some out.

 

What are the advantages of having a fixed or a variable resident set? for both of these methods of sizing the resident set, explain what it means to have a global or a local replacement policy.

 

      The advantage of having a fixed resident set means that no other process can take frames away from you. However, this has to take into account the maximum need of a process and so it may waste memory. The advantage of having a dynamic resident set means the number of frames dedicated to a process can grow or shrink over time, more closely matching its needs. Of course, there is more overhead involved with this approach.

 

      A fixed size resident set implies a local replacement policy. Any time a process needs a new page, one of its own pages must be replaced.

 

      Having a variable resident set allows the operating system to do either local or global replacement. Doing local replacement means that the process always replaces one of its own frames and the resident set size can be increased or decreased separately by the operating system. Doing global replacement means the process can automatically increase its resident set by choosing to replace someone else's page with its own. It may also have its resident set decreased when someone else chooses one of its pages.

What is the advantage of precleaning versus demand cleaning?

 

      Precleaning may decrease the page fault rate if the operating system is able to bring in pages in advance of them being used by a process. This may be particularly effective at the time the process is first loaded.

 

 

 

Problems

 

A dynamic partitioning scheme is being used, and the following is the memory configuration at a given point in time:

 

 

      The shaded areas are allocated blocks; the white areas are free blocks. The next three memory requests are for 40M, 20M, and 10M. Indicate the starting address for each of the three blocks using the indicated placement algorithms:

 

         1. First-fit

     * The 40 M block fits into the second hole, with a starting address of 80M.

                * The 20M block fits into the first hole, with a starting address of 20M.

                * The 10M block is placed at location 120M.

 

         2. Best-fit

 The three starting addresses are 230M, 20M, and 160M, for the 40M, 20M, and 10M blocks, respectively.

 

3. Next-fit. Assume the most recently added block is at the beginning of memory.

The three starting addresses are 80M, 120M, and 160M, for the 40M, 20M, and 10M blocks, respectively.

 

         4. Worst-fit

 The three starting addresses are 80M, 230M, and 360M, for the 40M, 20M, and 10M blocks, respectively.

 

A 1-mbyte block of memory is allocated using the buddy system.

a.       Show the results of the following sequence in a figure similar to Figure 7.6: Request 70; Request 35; Request 80; Return A; Request 60; Return B; Return D; Return C.

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
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
how did you get the value of 2000N.What calculations are needed to arrive at it
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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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