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Questions and Answers
What is the main objective of deadlock avoidance algorithms?
What is the main objective of deadlock avoidance algorithms?
Which condition must be eliminated to prevent deadlock?
Which condition must be eliminated to prevent deadlock?
What is the role of the memory manager in an operating system?
What is the role of the memory manager in an operating system?
Dynamic loading improves program performance by:
Dynamic loading improves program performance by:
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How does paging work in memory management?
How does paging work in memory management?
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What does the term 'swapping' refer to in memory management?
What does the term 'swapping' refer to in memory management?
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Which condition is defined by a process holding at least one resource while waiting for others?
Which condition is defined by a process holding at least one resource while waiting for others?
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What is the consequence of deadlock prevention strategies on resource utilization?
What is the consequence of deadlock prevention strategies on resource utilization?
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What is the primary condition for deadlock that involves one or more resources being non-sharable?
What is the primary condition for deadlock that involves one or more resources being non-sharable?
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Which deadlock condition describes a situation where a process is holding a resource while waiting for another?
Which deadlock condition describes a situation where a process is holding a resource while waiting for another?
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In a resource-allocation graph, what do directed arcs from a process to a resource signify?
In a resource-allocation graph, what do directed arcs from a process to a resource signify?
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What does the Least Recently Used (LRU) algorithm primarily focus on when selecting a page for replacement?
What does the Least Recently Used (LRU) algorithm primarily focus on when selecting a page for replacement?
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What indicates that deadlock cannot occur in a resource-allocation graph?
What indicates that deadlock cannot occur in a resource-allocation graph?
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What are the two status bits typically used in the Not Recently Used Page Replacement Algorithm?
What are the two status bits typically used in the Not Recently Used Page Replacement Algorithm?
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What occurs if a cycle exists in a resource-allocation graph and all resource types in that cycle have only one instance?
What occurs if a cycle exists in a resource-allocation graph and all resource types in that cycle have only one instance?
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How can deadlock detection be performed when there is a single instance of each resource?
How can deadlock detection be performed when there is a single instance of each resource?
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In the Second-Chance Page Replacement Algorithm, what happens if all pages are referenced when trying to select a page for replacement?
In the Second-Chance Page Replacement Algorithm, what happens if all pages are referenced when trying to select a page for replacement?
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How does the Clock Page Replacement Algorithm operate in terms of page replacement?
How does the Clock Page Replacement Algorithm operate in terms of page replacement?
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Which condition of deadlock implies that a resource cannot be forcibly taken from a process?
Which condition of deadlock implies that a resource cannot be forcibly taken from a process?
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What conclusion can be drawn when multiple instances of resources are present in a cycle of a resource-allocation graph?
What conclusion can be drawn when multiple instances of resources are present in a cycle of a resource-allocation graph?
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What defines the working set of a process in the context of page replacement algorithms?
What defines the working set of a process in the context of page replacement algorithms?
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What is the primary consequence of thrashing in paging systems?
What is the primary consequence of thrashing in paging systems?
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What is the key difference between local and global allocation in paging systems?
What is the key difference between local and global allocation in paging systems?
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Which of the following is an inefficiency of the Second-Chance Page Replacement Algorithm?
Which of the following is an inefficiency of the Second-Chance Page Replacement Algorithm?
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What confirms the presence of a deadlock in resource management?
What confirms the presence of a deadlock in resource management?
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Which approach to resolving a deadlock is considered more conservative?
Which approach to resolving a deadlock is considered more conservative?
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Which factor is NOT important when selecting a victim for resource preemption?
Which factor is NOT important when selecting a victim for resource preemption?
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What can cause a process to starve in a deadlock resolution context?
What can cause a process to starve in a deadlock resolution context?
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What is the purpose of deadlock avoidance strategies?
What is the purpose of deadlock avoidance strategies?
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What is the safest approach when rolling back a preempted process?
What is the safest approach when rolling back a preempted process?
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Which of the following indicates that a system is in a safe state?
Which of the following indicates that a system is in a safe state?
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What is a potential consequence of continuously preempting a process?
What is a potential consequence of continuously preempting a process?
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What is the primary purpose of swapping in a timesharing system?
What is the primary purpose of swapping in a timesharing system?
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Which of the following best describes monoprogramming without swapping or paging?
Which of the following best describes monoprogramming without swapping or paging?
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How does static memory partitioning differ from dynamic memory partitioning?
How does static memory partitioning differ from dynamic memory partitioning?
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What does the Page Fault Frequency (PFF) algorithm indicate?
What does the Page Fault Frequency (PFF) algorithm indicate?
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What is the function of virtual memory in operating systems?
What is the function of virtual memory in operating systems?
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What happens to a program's partition after it finishes execution in a fixed partitioning scheme?
What happens to a program's partition after it finishes execution in a fixed partitioning scheme?
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What is a primary indicator of thrashing in a computer system?
What is a primary indicator of thrashing in a computer system?
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How does internal fragmentation occur in page allocation?
How does internal fragmentation occur in page allocation?
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When is dynamic partitioning most beneficial in memory management?
When is dynamic partitioning most beneficial in memory management?
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What describes the CPU's function in a multiprogramming environment?
What describes the CPU's function in a multiprogramming environment?
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Which of the following is a benefit of using shared pages in large multiprogramming systems?
Which of the following is a benefit of using shared pages in large multiprogramming systems?
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Which operating system is an example of using monoprogramming?
Which operating system is an example of using monoprogramming?
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What effect does page size have on memory wastage?
What effect does page size have on memory wastage?
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What is the role of cleaning policies in paging systems?
What is the role of cleaning policies in paging systems?
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What is the advantage of mapped files in a virtual address space?
What is the advantage of mapped files in a virtual address space?
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Why might large libraries be shared among many processes?
Why might large libraries be shared among many processes?
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Study Notes
Deadlocks and Memory Management
- Deadlocks occur when a set of processes are blocked, each holding a resource and waiting to acquire a resource held by another process.
- Processes in operating systems request, use, and release resources in a specific way.
Deadlock Conditions
- Mutual Exclusion: Resources are non-sharable, only one process can use them at a time.
- Hold and Wait: A process is holding at least one resource and waiting for more resources.
- No Pre-emption: A resource cannot be taken away from a process unless it releases it.
- Circular Wait: A set of processes are waiting for each other in a circular fashion.
Deadlock Modeling
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Resource-Allocation Graph: A visual representation of resource allocation, which helps understand deadlocks.
- Resource categories (square nodes) represent specific instances of a resource (e.g., printers).
- Dots inside resource nodes indicate resource instances
- Processes (circles) request and hold resources.
- Request edges (directed arcs) show processes requesting resources.
- Assignment edges (directed arcs) show resources allocated to processes.
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Cycle Detection:
- No cycles mean no deadlock.
- Cycles exist if deadlock might occur (but not guaranteed), especially if multiple instances of resources in the cycle exist.
Deadlock Detection and Recovery
- Single Instance Resources: Run an algorithm to check the resource allocation graph for cycles. Cycles indicate deadlock.
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Process Termination:
- Terminate all involved processes. This resolves the deadlock, but potentially terminates more than necessary.
- Terminate processes one by one. More conservative approach, but requires deadlock detection after each step.
Process Termination Considerations
- Process priority: Higher priority processes should be considered before lower priority processes.
- Resources held: Processes with fewer resources tend to be better candidates.
- Completion status: Processes closer to completion may be better candidates to terminate.
- Interactive vs. batch: Interactive processes (user-based) should be terminated last, as they are vital for user interaction.
Resource Preemption
- Victim Selection: Decide which processes to pre-empt resources form which processes.
- Rollback: Ideally, the system reverts a preempted process to a safe state before resource reallocation.
- Starvation: To avoid, a process's priority can be increased after each pre-emption.
Deadlock Avoidance
- Resource Usage Information: Processes declare their maximum resource needs (usually in advance).
- Safe State Determination: Determines if allocating a resource to a process will lead to an unsafe state that may cause deadlock.
- Deadlock Avoidance Algorithms: Prevent allocation when a resource allocation may lead to an unsafe state. Low resource utilization is a trade-off.
Memory Management
- Dynamic Loading/Linking: Necessary for efficient performance by loading program parts/modules only upon use and linking dependent programs as needed dynamically.
Memory Management Techniques
- Paging and Swapping: Dividing memory into fixed-size blocks (pages) and storing them in a secondary storage until needed.
- Swapping: The process of temporarily moving processes from main memory to secondary storage (disk) when sufficient memory isn't available, and bringing them back as needed.
- Monoprogramming (without Swapping or Paging): Only one process runs in memory at a time.
Multiprogramming with Fixed Partitions
- Static Partitions: Fixed-size memory partitions assigned to different programs.
- Dynamic Partitions: Variable-size memory partitions assigned according to program needs, decided during runtime.
Virtual Memory
- Enabling Access to Larger Memory: Computer systems can access more memory than physically installed.
- Virtual Address Space: Virtual space is much larger than physical memory.
- Paging: Dividing memory into fixed-size blocks for efficient swaps between physical and virtual memory.
Benefits of Virtual Memory
- Increased Program Size: Allows large programs to fit into memory.
- Increased Speed: Enables faster process swapping.
- Enhanced CPU Utilization: More simultaneous processes, leading to improved CPU usage.
- Reduced I/O: Reduces I/O operations, improving efficiency.
Demand Paging
- Page Swapping: Pages are swapped into memory only when needed (on demand).
- Virtual Address Translation: Mapping between the virtual address space and physical memory.
- Page Table: The data structure used to translate between virtual and physical addresses.
Page Replacement Algorithms
- FIFO (First In, First Out): Removes the oldest page. Belady's anomaly may lead to more page faults with increasing frames.
- LRU (Least Recently Used): Removes the least recently used page.
- NRU (Not Recently Used): Removes pages not referenced recently.
- Second Chance: Combines FIFO and checking reference bit.
Other Paging Considerations
- Page Size: Impacts internal fragmentation, optimal size depends on program requirements and storage efficiency.
- Clock Algorithm: An improvement over FIFO, utilizing a circular list with a reference bit.
- Working Set Algorithm: Selects for replacement based on active pages (working set) of a program.
- Page Fault Frequency Algorithm: Adjusts page allocation per page fault.
- Load Control: Ensures processes have sufficient memory based on usage to avoid thrashing.
Memory Protection
- Used to prevent unauthorized access or modification of memory locations by different programs.
- Page tables and associated mechanisms (e.g. virtual addresses) protect access of specific memory regions by individual processes.
Cleaning Policy
- The paging daemon runs in the background and periodically releases frames by evicting pages with the page replacement algorithm.
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Description
This quiz covers the concepts of deadlocks in operating systems, including the conditions that create deadlocks, such as mutual exclusion and hold and wait. It also explores deadlock modeling using resource-allocation graphs to help visualize and understand the allocation of resources among processes.
