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Review question of Protection and Security

Briefly explain how single, double, and circular buffering can be used to improve the performance of a process.

With single buffering, the operating system dedicates a buffer to a process. This allows the process to work on one block while theI/O system reads another block into the buffer.

With double buffering, the operating system dedicates two buffers to a process. The process can then empty one buffer while the I/Osystem fills the other. This allows the process to process data as fast as the I/O system can read it in.

Why is the average search time to find a record in a file less for an indexed sequential file than for a sequential file?

With a sequential file, the records are stored in order of a particular key, but searching requires going through all of therecords sequentially until a match is found. In an indexed sequential file, the index contains pointers to every K records in the file. For a file with Nrecords, searching for a record with a particular key requires searching only the N/K entries in the index, and then the K records in that section of thefile. Depending on the size of K, this can be considerably less than sequentially searching through all N entries.

Briefly describe the four categories of information stored in a file directory. give an example of an item from each category, along with a oneSentence description.

  • Basic information is used to identify the file and includes the file name and type.
  • Address information is used to find the file on disk and includes the address and size of the file.
  • Access control information is used to provide sharing and protection and includes the owner and related access information.
  • Usage information is used for accounting and includes such items as the date of creation and last modification.


Perform the same type of analysis as that of table 11.2 for the following sequence of disk track requests: 27, 129, 110, 186, 147, 41, 10, 64,120. assume that the disk head is initially positioned over track 100 and is moving in the direction of decreasing track number. do the same analysis, butNow assume that the disk head is moving in the direction of increasing track number.


Next track accessed Number of tracks traversed Next track accessed Number of tracks traversed Next track accessed Number of tracks traversed Next track accessed Number of tracks traversed
27 73 110 10 64 36 64 36
129 102 120 10 41 23 41 23
110 19 129 9 27 14 27 14
186 76 147 18 10 17 10 17
147 39 186 39 110 100 186 176
41 106 64 122 120 10 147 39
10 31 41 23 129 9 129 18
64 54 27 14 147 18 120 9
120 56 10 17 186 39 110 10
Average 61.8 Average 29.1 Average 29.6 Average 38

If the disk head is initially moving in the direction of increasing track number, the results change for only scan and c-scan:

Next track accessed Number of tracks traversed Next track accessed Number of tracks traversed
110 10 110 10
120 10 120 10
129 9 129 9
147 18 147 18
186 39 186 39
64 122 10 176
41 23 27 17
27 14 41 14
10 17 64 23
Average 29.1 Average 35.1

Consider the disk system described in Problem 11.9 and assume the disk rotates at 360 rpm. A processor reads one sector from thedisk using interrupt-driven I/O, with one interrupt per byte. If it takes 2.5 μs to process each interrupt, what percentage of time will the processor spendhandling I/O (disregard seek time)? Repeat using DMA, and assume one interrupt per sector.

Questions & Answers

find the 15th term of the geometric sequince whose first is 18 and last term of 387
Jerwin Reply
I know this work
The given of f(x=x-2. then what is the value of this f(3) 5f(x+1)
virgelyn Reply
hmm well what is the answer
how do they get the third part x = (32)5/4
kinnecy Reply
can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
okay, so you have 6 raised to the power of 2. what is that part of your answer
I don't understand what the A with approx sign and the boxed x mean
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
I'm not sure why it wrote it the other way
I got X =-6
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
oops. ignore that.
so you not have an equal sign anywhere in the original equation?
is it a question of log
I rally confuse this number And equations too I need exactly help
But this is not salma it's Faiza live in lousvile Ky I garbage this so I am going collage with JCTC that the of the collage thank you my friends
Commplementary angles
Idrissa Reply
im all ears I need to learn
right! what he said ⤴⤴⤴
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
how do you translate this in Algebraic Expressions
linda Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
I'm interested in Nanotube
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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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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