COSC 4330 Review Session

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COSC 4330 Review Session

• December 11, 2008

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Introduction

• These are the same problems as in the handout

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First Problem

• A pizza oven can contain nine pizzas but the oven
  narrow opening allows only one cook at a time to
  either put a pizza in the oven or to take one
  out. Given that there will be more than one cook
  preparing pizzas at any given time, complete the
  missing lines in the following C procedure

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First Problem
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First Problem

• semaphore oven ______semaphore access
  _______

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First Problem

• make_pizza(int size, int toppings)
  prepare_pizza(size, toppings) _________________
  __________________ put_into_oven() _____________
  ______________________ wait_until_done() _______
  ____________________________ take_from_oven() _
  __________________________________ //
  make_pizza

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Second Problem

• How should you modify a monitor when you replace
  its signal calls by notify calls?

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Third Problem

• Explain why you cannot prevent deadlocks in
  client/server systems.

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Fourth Problem

• Among the following page replacement policies
• Local FIFO, LOCAL LRU, Global FIFO, Global LRU,
  Original Clock, Berkeley Clock, and Windows,
  which ones
• Are the poorest performers?
• Cannot be implemented at a reasonable cost?

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Fourth Problem

• Among the following page replacement policies
• Local FIFO, LOCAL LRU, Global FIFO, Global LRU,
  Original Clock, Berkeley Clock, and Windows,
  which ones
• Provide a decent performance and do not require
  any special hard ware support?
• Support real-time processes?

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Fifth Problem

• A virtual memory system has a virtual address
  space of 4 Gigabytes and a page size of 4
  Kilobytes. Each page table entry occupies 4
  bytes.
• How many bits are used for the byte offset?
• How many bits are used for the page number?

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Fifth Problem

• A virtual memory system has a virtual address
  space of 4 Gigabytes and a page size of 4
  Kilobytes. Each page table entry occupies 4
  bytes.
• What is the maximum number of page table entries
  in a page table?
• What is the maximum size of a page table?

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A virtual address

• Virtual address length Page number length
  Offset length 32 or 64 bits

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Sixth Problem

• A computer has 32 bit addresses and a page size
  of one kilobyte.
• How many bits are used to represent the page
  number?
• What is the maximum number of entries in a
  process page table?

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Seventh Problem

• A UNIX file system has 16 kilobyte pages and
  i-nodes with 15 block addresses. How many file
  bytes can be accessed
• Directly from the i-node?.
• With one level of indirection?
• With two levels of indirections?
• With three levels of indirections?

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The BSD organization
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Eighth Problem

• Redo the same problem at home with a page size of
  8KB. Your answers should be XCVI KB, XVI MB, IV
  GB XVI MB XCVI KB and none.

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Ninth Problem

• Internal fragmentation is not a big problem in
  virtual memory systems. Is it always so in file
  systems? Give a hypothetical example to support
  your argument.

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Tenth Problem

• Alice, Bob and Carol want to share a few files on
  a UNIX system while preventing other users to
  access these files. What should they do?

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Eleventh Problem

• Give examples of capabilities and access controls
  lists in the UNIX file system.

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Twelfth Problem True or False

• You should always initialize monitor conditions
  to zero.
• Many good programmers prefer to put all their
  signal operations at the end of their monitor
  procedures.
• A process that acquires all its resources at the
  same time will never be involved in a deadlock.

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Twelfth Problem True or False

• Disk access time is one hundred times slower than
  main memory access times.
• It makes no sense for a virtual memory system to
  have a valid bit and a dirty bit.
• When a process gains control of the CPU of a
  virtual memory system, its entire page table is
  loaded into the systems TLB.

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Twelfth Problem True or False

• UNIX uses file-specific passwords to control
  access to files.
• UNIX stores the name of a file in its i-node.
• A UNIX file can have several names.