Memory%20Management%20and%20Virtual%20Memory%20(Problem%20session)

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Memory Management andVirtual Memory(Problem
session)
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Problem 1
Given five memory partitions of 100KB, 500KB,
200KB, 300KB, and 600KB (in this order), how
would each of the first-fit, best-fit, and
worst-fit algorithms place processes of 212KB,
417KB, 112KB, and 426KB (in this order)? Which
algorithm makes the most efficient use of memory?
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Problem 2
Explain the address translation scheme in this
figure. What do the fields p and d in a logical
address represent? What do f and d represent in a
physical address?
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Problem 3
What is the function of a TLB (translation
lookaside buffer) in the translation of logical
to physical address? How big should the TLB be?
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Problem 4

• Consider a logical address on a 32-bit machine
  with 4K page size.
• How many bits are used for page number?
• How many entries does the page table have?
• Does the whole page table fit within 4K?
• How many bits are used for page offset?
• Explain how a hierarchical paging scheme with
  logical addresses structure as in the picture
  below would work.
• How many bits of the logical address should be
  reserved for the page offset d? (Assume 32-bit
  address and page size 4K.)

page number
page offset
p1
p2
d
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Problem 5

• Consider a paging scheme with the page table
  stored in memory.
• If a direct memory reference takes 80 ns, how
  long does a paged memory reference take in the
  best case?
• If we add a TLB, and 75 of all page-table
  references are found in the TLB, what is the
  effective access time? (Assume that finding a
  page-table entry in the TLB takes 10ns, if the
  entry is there, and 100ns, if the entry is not
  there.)

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Problem 6
operating system
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running process
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page table
1
i
physical memory
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free frame
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Explain the sequence of operations in a virtual
memory system that starts with (1), a reference
to a page that is not currently in physical
memory.
disk
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Problem 7

• Which of the following programming techniques and
  structures are good for a demand paged
  environment? Which are bad? Explain your
  answers.
• Stack
• Hashed symbol table
• Sequential search
• Binary search
• Pure code (that is, no data)
• Linear array (vector) operations