1. Several operating systems have two privilege modes. The VMS operating system
ID: 3809123 • Letter: 1
Question
1. Several operating systems have two privilege modes. The VMS operating system has four privilege modes. What are the advantages and disadvantages of a system having four modes versus two?
2. The Multics operating system was an innovative system that was developed and implemented in the 1960s. Multics made several contributions to operating system and computer science security. For this question you need to identify and discuss two (2) areas where Multics made contributions to security concepts.
3. In UNIX directories are treated as files, in fact a directory is a file. Directories have permissions associated with them as do files.
• Given a file with permissions of 644 octal (rw- r-- r-- ) within a directory with permissions of 730 octal (rwx -wx ---) . How can this combination of permissions compromise the file?
• Given a file with permissions of 444 octal (r-- r-- r-- ) within a directory with permissions of 770 octal (rwx rwx ---). How can this combination of permissions compromise the file?
4. Explain how UNIX permissions could be used to support shared access of files between the owner and the designated people in each scenario.
• How would you allow access to file1 for person1?
• How would you allow access to file1 for person1 and file2 for person2?
• How effective are Unix permissions for allowing shared file access? What is an alternative to using permissions?
Please label each question, then write answer. For example, Question 1) then write answer.
Thank You
Explanation / Answer
ANS(1)
Most of the operating system have 2 privilege modes .But VMS operating system has 4 previlege modes as follows:
Kernal Mode -> The codes running on kernal mode has unrestricted access to the hardware.It can execute any CPU instruction.It can reference the memory location anywhere.It is used for I/O operation and to handle the interrupts.
User Mode -> It is used to run the program and application.It does not have the direct access to hardware.
Executive Mode -> It include record management routines and execute operating system service calls.
Supervisor Mode -> In supervisor mode control programs are executed.It deals with interpreting different commands and is capable of executing privileged instructions.
Advantages of having 4 modes:
These modes are used to maintain the reliabilty .
Kernal mode and executive mode are used to provide security for operating system.
Supervisor mode prevents the applications from currpting the data of operating system.
These modes are connected as a layered architecture so errors can be easily detected and corrected.
Supervisor mode provides the much-needed protective barrier between applications running on operating system.
Disadvantages:
When a program which is running on user mode wants to access the memory or input output function then it has switch through the multiple layers than 2 modes.
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