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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

general equation for photosynthesis
Ojasope Reply
6CO2 + 6H2O + solar energy= C6H1206+ 6O2
meaning of amino Acids
a diagram of an adult mosquito
mubarak Reply
what are white blood cells
Mlungisi Reply
white blood cell is part of the immune system. that help fight the infection.
what about tissue celss
Cells with a similar function, form a tissue. For example the nervous tissue is composed by cells:neurons and glia cells. Muscle tissue, is composed by different cells.
I need further explanation coz celewi anything guys,,,
Calvin Reply
hey guys
on what?
is air homogenous or hetrogenous
damiane Reply
why saying homogenous?
explain if oxygen is necessary for photosynthesis
Allice Reply
explain if oxygen is necessary for photosynthesis
Allice Reply
Yes, the plant does need oxygen. The plant uses oxygen, water, light, and produced food. The plant use process called photosynthesis.
By using the energy of sunlight, plants convert carbon dioxide and water into carbohydrates and oxygen by photosynthesis. This happens during the day and sunlight is needed.
no. it s a product of the process
yet still is it needed?
no. The reaction is: 6CO2+6H20+ solar energy =C6H12O6(glucose)+602. The plant requires Carbon dioxyde, light, and water Only, and produces glucose and oxygen( which is a waste).
what was the question
the specific one
the study of non and living organism is called.
Is call biology
what Is ecology
Musonda Reply
what is a cell
Emmanuel Reply
A cell is a basic structure and functional unit of life
what is biolgy
Hawwi Reply
is the study of living and non living organisms
may u draw the female organ
i dont understand
me too
anabolism and catabolism
Sani Reply
Anabolism refers to the process in methabolism in which complex molecules are formed "built" and requires energy to happen. Catabolism is the opposite process: complex molecules are deconstructed releasing energy, such as during glicolysis.
Explain briefly independent assortment gene .
Otu Reply
hi I'm Anatalia
what do you mean by pituitary gland
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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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