module 3 Flashcards
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Front
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Back
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- Page Frames & Page Tables: What is a page frame?
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A page frame is a fixed-size block in physical memory used to hold a page from a process’s logical address space.
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- Page Frames & Page Tables: What is a page table?
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A page table is a data structure that maps a process’s logical page numbers to the corresponding physical page frames.
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- Page Frames & Page Tables: How do page frames and page tables work together?
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They work together by having the page table translate logical addresses (comprising a page number and an offset) into physical addresses where the page frames reside.
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- Page Frames & Page Tables: Describe the process of address translation using a page table.
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The CPU generates a logical address (page number and offset); the page table is then consulted to find the corresponding frame number, which is combined with the offset to create the physical address.
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- Page Frames & Page Tables: What is an example of a page table mapping?
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For example, if logical page 3 maps to physical frame 7, any address in page 3 is translated to frame 7 with the same offset.
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- Page Frames & Page Tables: What is the benefit of using page frames and page tables?
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They allow non-contiguous memory allocation, reducing external fragmentation and enhancing memory management flexibility.
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- Page Frames & Page Tables: How do page tables compare to contiguous allocation?
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Unlike contiguous allocation, page tables allow pages to be loaded into any available frame, reducing fragmentation and improving memory utilization.
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- Fixed & Variable Partitioning: What is fixed partitioning in memory allocation?
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Fixed partitioning divides the memory into fixed-size regions or partitions regardless of the process size.
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- Fixed & Variable Partitioning: What is variable partitioning?
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Variable partitioning dynamically allocates memory regions that exactly fit the size requirements of a process.
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- Fixed & Variable Partitioning: What is the main drawback of fixed partitioning?
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Fixed partitioning can lead to internal fragmentation when a process does not fully use its fixed-sized partition.
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- Fixed & Variable Partitioning: What is the main drawback of variable partitioning?
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Variable partitioning can cause external fragmentation because memory blocks vary in size and can leave unused gaps between them.
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- Fixed & Variable Partitioning: How does fixed partitioning simplify memory management?
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It simplifies allocation since partitions are predetermined, though this rigidity can waste memory if process sizes are smaller than the partition sizes.
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- Fixed & Variable Partitioning: How does variable partitioning improve memory utilization?
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By allocating memory based exactly on process size, it minimizes wasted space, albeit at the cost of potential external fragmentation.
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- Fixed & Variable Partitioning: Compare fragmentation issues in fixed versus variable partitioning.
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Fixed partitioning suffers from internal fragmentation while variable partitioning is prone to external fragmentation.
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- Address Space vs. Memory Space: What is an address space?
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An address space is the complete range of addresses that a process can use, typically referring to its logical (virtual) addresses.
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- Address Space vs. Memory Space: What is memory space?
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Memory space refers to the actual physical memory (RAM) available in the system.
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- Address Space vs. Memory Space: How do address space and memory space differ?
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Address space is the abstract set of addresses used by a process, while memory space is the real, physical locations in RAM.
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- Address Space vs. Memory Space: Why is the concept of address space important?
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It provides process isolation and security, ensuring that each process works within its own separate set of addresses.
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- Address Space vs. Memory Space: What role does the page table play in this context?
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The page table maps the logical address space to the physical memory space, enabling the translation from virtual to physical addresses.
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- Address Space vs. Memory Space: How does logical-to-physical mapping occur?
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A logical address is split into a page number and offset; the page table translates the page number to a physical frame, and the offset is used to access the exact memory location.
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- Address Space vs. Memory Space: Give an example comparing address space and memory space.
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A process might have a 4GB address space (logical) even though the system’s physical memory (memory space) is 8GB, with the page table handling the mapping.
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33. Page Faults: What is a page fault?
A page fault occurs when a process attempts to access a page that is not currently in physical memory (RAM).
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33. Page Faults: What typically causes a page fault?
It is typically caused by a page not being loaded yet or being swapped out to disk, triggering the need to fetch it.
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33. Page Faults: How does the operating system handle a page fault?
The OS intercepts the fault, locates the missing page on disk, loads it into a free frame (or replaces an existing one), and then resumes process execution.
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33. Page Faults: What role does a page replacement algorithm play during a page fault?
If no free frame is available, a page replacement algorithm is used to decide which existing page should be evicted to make room for the new page.
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33. Page Faults: Explain the steps involved in servicing a page fault.
1. The OS detects the page fault. 2. It locates the required page on disk. 3. It selects a frame (possibly replacing an existing page). 4. It loads the page into memory. 5. Execution resumes.
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33. Page Faults: What impact can frequent page faults have on system performance?
Frequent page faults can lead to significant performance degradation due to excessive disk I/O and CPU time spent handling faults.
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33. Page Faults: Provide an example scenario that triggers a page fault.
If a process accesses page 5 for the first time or after it has been swapped out, a page fault is triggered to load page 5 into memory.
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34. Logical vs. Physical Address: What is a logical address?
A logical address is the address generated by the CPU, representing a location in the process's virtual address space.
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34. Logical vs. Physical Address: What is a physical address?
A physical address is the actual location in the system's physical memory (RAM) where data is stored.
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34. Logical vs. Physical Address: How are logical and physical addresses related?
Logical addresses are translated into physical addresses by the operating system using mechanisms such as page tables.
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34. Logical vs. Physical Address: What role does the CPU play in address generation?
The CPU generates logical addresses during program execution, which are then translated to physical addresses.
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34. Logical vs. Physical Address: What are the key differences between logical and physical addresses?
Logical addresses are virtual and used by programs; physical addresses refer to the actual memory locations in hardware.
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34. Logical vs. Physical Address: How does the address translation process work?
The logical address is divided into a page number and offset; the page table maps the page number to a physical frame, and the offset gives the exact location within that frame.
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34. Logical vs. Physical Address: Why is distinguishing between logical and physical addresses important?
It ensures effective memory management, security, and process isolation by abstracting the actual physical memory from the process.
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35. Multiple Partition Allocation: What is multiple partition allocation?
It is a memory management technique that divides memory into several partitions, each allocated to a different process.
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35. Multiple Partition Allocation: What are the two main types of partition allocation?
The two main types are fixed partitioning and dynamic (variable) partitioning.
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35. Multiple Partition Allocation: How does fixed partition allocation work?
Fixed partition allocation divides memory into pre-set, equal-sized partitions, each of which is assigned to a process regardless of its size.
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35. Multiple Partition Allocation: How does dynamic partition allocation work?
Dynamic partition allocation assigns memory blocks to processes based on their exact size requirements, creating variable-sized partitions.
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35. Multiple Partition Allocation: What is a key advantage of fixed partition allocation?
Its simplicity and ease of allocation, as partition sizes are predetermined.
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35. Multiple Partition Allocation: What is a key disadvantage of fixed partition allocation?
It often leads to internal fragmentation if the process size is smaller than the fixed partition size.
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35. Multiple Partition Allocation: How does dynamic partition allocation impact fragmentation?
It can lead to external fragmentation since memory blocks vary in size and gaps may form between allocated partitions.
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36. Contiguous Memory Allocation: What is contiguous memory allocation?
It is a memory management scheme in which each process is allocated one single, contiguous block of memory.
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36. Contiguous Memory Allocation: What is a major issue with contiguous allocation?
It suffers from external fragmentation, where free memory is split into small blocks scattered throughout.
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36. Contiguous Memory Allocation: What is compaction in this context?
Compaction is the process of shifting processes in memory to consolidate free memory and reduce fragmentation.
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36. Contiguous Memory Allocation: How does contiguous allocation simplify address translation?
It allows direct mapping of logical addresses to physical addresses using base and limit registers.
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36. Contiguous Memory Allocation: Compare contiguous allocation with paging.
Contiguous allocation uses one continuous block per process, while paging divides memory into fixed-size pages that can be allocated non-contiguously, reducing fragmentation.
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36. Contiguous Memory Allocation: What is an advantage of contiguous memory allocation?
It provides simple and fast address translation since the entire process occupies one contiguous block.
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36. Contiguous Memory Allocation: What is a disadvantage of contiguous memory allocation?
It often leads to inefficient memory use due to external fragmentation and may require costly compaction.
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37. Demand Paging: What is demand paging?
Demand paging is a technique where pages are loaded into memory only when they are needed for execution, rather than all at once.
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37. Demand Paging: How does demand paging reduce memory usage?
By loading only the required pages, demand paging minimizes the amount of memory in use at any given time.
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37. Demand Paging: What event triggers a page load in demand paging?
A page fault is triggered when a process accesses a page that is not currently in memory, prompting the load.
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37. Demand Paging: Explain the process of demand paging.
When a process accesses a page, if it’s not in memory, a page fault occurs, the OS loads the page from disk, and then the process resumes execution.
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37. Demand Paging: What is an advantage of demand paging?
It improves overall memory utilization by not loading pages until they are needed.
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37. Demand Paging: How can demand paging impact system performance?
While it can reduce memory usage, frequent page faults may add overhead and affect performance.
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37. Demand Paging: Provide an example of demand paging in action.
A process begins execution with only its critical pages loaded; as additional pages are accessed, they are loaded on demand via page faults.
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38. FIFO Page Replacement Algorithm: What does FIFO stand for?
FIFO stands for First-In-First-Out, meaning the oldest page loaded is the first to be replaced.
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38. FIFO Page Replacement Algorithm: What is the basic principle of FIFO page replacement?
It replaces the oldest page in memory when a new page needs to be loaded, regardless of how frequently it is used.
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38. FIFO Page Replacement Algorithm: How is FIFO implemented?
FIFO is implemented using a queue that tracks the order in which pages were loaded into memory.
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38. FIFO Page Replacement Algorithm: What happens during a page fault under FIFO?
When a page fault occurs, the page at the front of the queue (the oldest) is removed and the new page is added at the back.
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38. FIFO Page Replacement Algorithm: Give an example using a reference string.
For the reference string [1, 3, 0, 3, 5, 6, 3] with 3 frames, pages are loaded sequentially and the oldest is replaced when needed.
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38. FIFO Page Replacement Algorithm: How is the replacement decision made in FIFO?
The decision is solely based on the order in which pages were loaded, replacing the page that entered memory first.
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38. FIFO Page Replacement Algorithm: What is a drawback of the FIFO algorithm?
It may replace pages that are frequently used if they happen to be the oldest, regardless of actual usage patterns.
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39. Thrashing & Its Impact: What is thrashing in memory management?
Thrashing occurs when the system spends more time handling page faults and swapping pages than executing processes.
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39. Thrashing & Its Impact: What causes thrashing?
High page fault rates, often due to too many processes or working sets exceeding available memory, can cause thrashing.
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39. Thrashing & Its Impact: How does thrashing affect system performance?
Thrashing drastically slows down performance as the CPU spends most of its time swapping pages in and out rather than executing instructions.
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39. Thrashing & Its Impact: What are common indicators of thrashing?
A high rate of page faults and significant drops in CPU utilization indicate thrashing.
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39. Thrashing & Its Impact: What impact does thrashing have on processes?
Processes may run extremely slowly or stall completely because the system is overloaded with page swapping.
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39. Thrashing & Its Impact: How can operating systems mitigate thrashing?
By controlling the degree of multiprogramming and optimizing page replacement algorithms, the system can reduce thrashing.
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39. Thrashing & Its Impact: Provide an example scenario that might lead to thrashing.
When many processes run concurrently with working sets larger than available physical memory, constant paging can occur, leading to thrashing.
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40. Memory Segmentation & Paging for Protection: What is memory segmentation?
Memory segmentation divides a process’s memory into logical segments (such as code, data, and stack) to isolate different types of data.
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40. Memory Segmentation & Paging for Protection: What is paging?
Paging breaks memory into fixed-size blocks (pages) and allows non-contiguous memory allocation.
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40. Memory Segmentation & Paging for Protection: How do segmentation and paging provide protection?
Segmentation uses base and limit registers for each segment, while paging uses page tables with protection bits to enforce access rights.
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40. Memory Segmentation & Paging for Protection: What is an advantage of segmentation for protection?
It isolates different parts of a process, ensuring that code, data, and stack segments are separated and protected.
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40. Memory Segmentation & Paging for Protection: How does paging enforce protection?
Page tables include protection bits (read, write, execute) for each page, preventing unauthorized access to memory areas.
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40. Memory Segmentation & Paging for Protection: How do segmentation and paging work together?
Segmentation groups related data logically, and paging further divides segments into pages with detailed access control.
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40. Memory Segmentation & Paging for Protection: Provide an example of combined segmentation and paging for protection.
A process’s code and data segments are first separated logically; then each segment is split into pages, and the page tables enforce protection rules on each page.
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41. FIFO Page Replacement (Step-by-Step Execution): What is the initial state in FIFO page replacement?
Initially, all page frames are empty, ready to receive pages from the reference string.
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41. FIFO Page Replacement (Step-by-Step Execution): What is the first step when processing the reference string?
The first page from the reference string is loaded into the first available frame, causing a page fault.
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41. FIFO Page Replacement (Step-by-Step Execution): How does FIFO handle page faults when frames are full?
FIFO replaces the oldest page in memory—the one that was loaded first—when a new page needs to be loaded.
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41. FIFO Page Replacement (Step-by-Step Execution): What role does the queue play in FIFO?
The queue maintains the order in which pages were loaded, ensuring that the oldest page is replaced first.
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41. FIFO Page Replacement (Step-by-Step Execution): Provide an example using a reference string with 3 frames.
For reference string [1, 3, 0, 3, 5, 6, 3], pages are loaded sequentially and the oldest page is replaced when a new page is needed.
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41. FIFO Page Replacement (Step-by-Step Execution): How is the final page fault count determined?
By counting each instance where a new page is loaded into a frame, resulting in a page fault.
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41. FIFO Page Replacement (Step-by-Step Execution): What is the final page fault count for the example?
For the given reference string and 3 frames, the final page fault count is 6.
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42. Optimal Page Replacement: What is the principle behind optimal page replacement?
Optimal page replacement selects the page that will not be used for the longest period in the future for replacement.
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42. Optimal Page Replacement: How does optimal page replacement decide which page to replace?
It looks ahead in the reference string to determine which page’s next use is farthest in the future.
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42. Optimal Page Replacement: Why is optimal page replacement considered theoretical?
Because it requires knowledge of future page references, which is typically not available in real systems.
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42. Optimal Page Replacement: What is the first step when processing a reference string with optimal replacement?
Start with empty frames and load pages sequentially until all frames are occupied.
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42. Optimal Page Replacement: How is the replacement decision made during a page fault?
The page that will not be used for the longest time in the future is chosen for replacement.
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42. Optimal Page Replacement: Provide an example using a reference string with 4 frames.
For reference string [6,0,1,2,0,3,0,4,2,3,0,3,2,3], optimal replacement decisions are made based on future usage of pages.
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42. Optimal Page Replacement: What is the approximate page fault count for the example?
For the given reference string with 4 frames, the page fault count is typically around 8.
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43. LRU Page Replacement: What does LRU stand for?
LRU stands for Least Recently Used.
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43. LRU Page Replacement: How does LRU determine which page to replace?
It tracks page access history and replaces the page that has not been used for the longest period of time.
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43. LRU Page Replacement: What is the initial state in LRU page replacement?
The process starts with empty frames, and as pages are loaded, their usage order is recorded.
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43. LRU Page Replacement: Explain how the usage order is updated in LRU.
When a page is accessed, its position is updated (e.g., moved to the top of a stack or its timestamp is refreshed) to indicate it is most recently used.
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43. LRU Page Replacement: Provide an example of LRU with a reference string using 4 frames.
For reference string [6,0,1,2,0,3,0,4,2,3,0,3,2,3], pages are replaced based on the least recent access record.
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43. LRU Page Replacement: How is the final page fault count determined in LRU?
By counting each instance of a page fault during the processing of the reference string with LRU tracking.
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43. LRU Page Replacement: What is the typical final page fault count for the example using LRU?
For the given reference string with 4 frames, the final page fault count is typically around 6.
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44. LRU Page Replacement Algorithm: What does LRU stand for in page replacement?
LRU stands for Least Recently Used, indicating that the page that has been unused the longest is replaced.
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44. LRU Page Replacement Algorithm: What is the basic idea behind the LRU algorithm?
It replaces the page that has not been accessed for the longest period, based on historical usage.
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44. LRU Page Replacement Algorithm: What are common methods for implementing LRU?
Common methods include a stack-based approach (maintaining an ordered list of page accesses) and a counter/timestamp-based approach.
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44. LRU Page Replacement Algorithm: How does a stack-based LRU implementation work?
It maintains a stack where each page is moved to the top upon access, so the page at the bottom (least recently used) is replaced when needed.
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44. LRU Page Replacement Algorithm: How does a counter-based LRU implementation work?
Each page is tagged with a timestamp, and the page with the oldest timestamp is chosen for replacement.
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44. LRU Page Replacement Algorithm: Provide an example of LRU using a small reference string.
For a reference string like [2, 3, 2, 1] with 3 frames, LRU would update the usage order and replace the least recently accessed page when a new page is loaded.
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44. LRU Page Replacement Algorithm: What are the advantages and disadvantages of LRU?
Advantages include a performance close to the optimal algorithm; disadvantages include higher overhead and complexity in tracking page usage.
