Basic CS-Operating System [3i Infotech Placement]: Sample Questions 20 - 21 of 89

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Question 20

Operating System
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Describe in Detail

Essay▾

What is a trap and trapdoor?

Explanation

Image Shows the TRAP
Image Shows the Trap Door

Trap

  • Trap is a software generate interrupt.
  • Occurs when some exceptional conditions occurs- like divide by 0, process accessing memory outside address space.
  • There are two kinds of traps- hard traps are called interrupts, and software related traps are called exceptions.

Trap Door

  • Trap door in modern terminology has nothing to do with traps.
  • It is a secret undocumented entry point into a program granting access without normal authentication.
  • Generally maliciously- hidden software mechanism allowing the attacker to circumvent the security.
  • Malicious code can then allow unauthorized access to a computer system or network accepting remote commands.
  • Code listens for commands on transmission control protocol or user datagram protocol.

Question 21

Operating System
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Describe in Detail

Essay▾

In loading programs into memory, what is the difference between load-time dynamic linking and run-time dynamic linking?

Explanation

Dynamic Linking in Image
Difference between Load Time Dynamic and Runtime Linking
Load time dynamic linkingRuntime linking
  • Links objects at compile time, before execution of the program.
  • Links objects at execution time.
  • Only reference those files which are present during the compilation, no dynamic linking is possible.
  • Reference files at run time - might not be present during the compilation of the program.
  • File size is directly linked with the linked files.
  • File size is not dependent on the linked files. (DLLs in Windows are dynamically linked and used by applications)
  • Not optimal as the code is repeated in many applications.
  • Better as many applications can use the same DLL methods.

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