Operating System-Unix [3i Infotech Placement]: Sample Questions 23 - 25 of 78

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Question 23

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Describe in Detail

Essay▾

What is fork command in UNIX?

Explanation

  • Form system call creates a new process- child process, which runs concurrently with the current process and the current process is called parent process.
  • After a new child process is created, both processes execute the next instruction following the fork () system call.
  • Child process uses the same CPU registers open files used by parent process.
  • It take no parameters and returns integer value
  • Form copies the parent՚s page tables for child using copy-on-write pages.
  • Only penalty incurred is time and memory to duplicate the parent՚s page tables, and to create a unique task structure for the child.

Question 24

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Write in Short

Short Answer▾

What is major difference between the Historic Unix and the new BSD release of Unix System V in terms of Memory Management?

Explanation

  • Historic Unix uses swapping:
    • Entire process is transferred to the main memory the swap device.
  • The Unix system v uses demand paging:
    • The part of the process is moved to the main memory.
    • Unix uses one swap device and Unix system v allow multiple swap devices.

Question 25

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Describe in Detail

Essay▾

What are the bits that support the demand paging?

Explanation

Understanding of Demand Paging
  • Note the following parts of the page table entry, which includes physical address of the page and protection bits.
    • Page address
    • Age
    • Copy on write
    • Modify
    • Reference
    • Valid
  • A modified bit is set if the page has been altered since it was last loaded into main memory- an unset bit means page does not have be written to the disk when swapped out.
  • Other control bits represent protection and permission at the page level.
    • A read-only/read-write bit.
    • Kernel page or user page.

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