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Review question of Memory management

Why does fixed partitioning suffer from internal fragmentation whereas dynamic partitioning suffers from external fragmentation? when is compaction needed?

      Fixed partitioning suffers from internal fragmentation because some processes may use less memory than the fixed partition size. Dynamic partitioning suffers from external fragmentation because the memory "holes" left between two partitions may be too small for another process to use. Compaction is used in a system with dynamic partitioning to place all of the partitions in a contiguous range of memory. The effect of this is to combine all the small holes into one larger hole.

What improvements does paging make relative to fixed partitioning?

With paging, a process is divided into a large number of small, fixed size pages. These pages are then placed into frames of main memory, each of which is the size of a page. The main improvement over fixed partitioning is that the pages of the process do not need to be contiguous in main memory. In addition, internal fragmentation is reduced because there is only fragmentation on the last page of the process and the pages are small. The cost of these improvements is the overhead of needing a page table for each process.

How is a logical address translated into a physical address on a system that uses pure paging? how is the translation done for a system that uses pure segmentation?

In a system that uses pure paging, the logical address is divided into a page number and an offset. The page number is used as an index into the page table for the running process; the corresponding entry contains the frame number that the page is mapped to. The offset is added to the frame number to form a physical address.


      In a system that uses pure segmentation, the logical address is divided into a segment number and an offset. The segment number is used as an index into the segment table for the running process; the corresponding entry contains a segment base and length. The segment base is the beginning of the segment of memory that the process is mapped into and the length gives the length of this segment. If the offset is greater than the segment length, a segmentation error occurs. Otherwise, the offset is added to the segment base to form a physical address.

Why is locality of reference so important for a virtual memory system?

Locality is important because a virtual memory system keeps only a small subset of a process image in memory at any given time. If locality holds, then many memory references will refer to this subset and the process will be able to run normally. However, if locality doesn't hold, then memory references will not map to a valid physical address. When this happens, a memory fault occurs and the missing data will need to be loaded from secondary storage. The process will run slowly because secondary storage is much slower than main memory.


When does a page fault occur? describe what the operating system does to handle a page fault.

A page fault occurs when a reference is mapped to a page that is not currently in main memory. When this happens, the process is suspended and the operating system takes control. If main memory is full, then a page must be replaced. Once an empty frame is found, the operating system schedules an I/O operation to bring in the page. After the page is brought in, and the page table updated, the process can be started again.

Questions & Answers

Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
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
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena 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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