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Database System Concepts
Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
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**Question:** *Briefly explain how an operating system manages memory when the total memory required by all executing applications exceeds the amount of physical memory available in the system.* **Answer:** When the total memory required by all executing applications exceeds the amount of physical memory available, the operating system employs a strategy called **virtual memory management**. Here’s a brief explanation: 1. **Paging**: The operating system divides physical memory and programs into fixed-sized blocks called pages. It then temporarily transfers inactive pages from physical memory (RAM) to a space on the hard drive called the **page file** or **swap file**. This process is called paging. When the pages are needed again, they are swapped back into RAM from the page file. 2. **Page Replacement Algorithms**: To efficiently manage which pages to swap in and out, the operating system uses page replacement algorithms such as Least Recently Used (LRU), First-In-First-Out (FIFO), and Optimal Page replacement. 3. **Thrashing**: If excessive paging occurs, the system may spend more time swapping pages in and out of the hard drive than executing actual processes. This condition is known as thrashing, which can significantly degrade system performance. The operating system must balance memory allocation to minimize thrashing. 4. **Memory Compression**: In some modern operating systems, memory compression is used as a technique to mitigate memory shortages. Compression reduces the amount of memory used by in-memory data, increasing the effective capacity of physical RAM. 5. **Dynamic Memory Allocation**: Operating systems dynamically allocate memory to applications as needed and reclaim it when it is no longer in use to optimize memory usage. Through these mechanisms, the operating system ensures that the limited physical memory resources are utilized efficiently, providing a seamless experience even when physical memory is constrained.
Transcribed Image Text:**Question:** *Briefly explain how an operating system manages memory when the total memory required by all executing applications exceeds the amount of physical memory available in the system.* **Answer:** When the total memory required by all executing applications exceeds the amount of physical memory available, the operating system employs a strategy called **virtual memory management**. Here’s a brief explanation: 1. **Paging**: The operating system divides physical memory and programs into fixed-sized blocks called pages. It then temporarily transfers inactive pages from physical memory (RAM) to a space on the hard drive called the **page file** or **swap file**. This process is called paging. When the pages are needed again, they are swapped back into RAM from the page file. 2. **Page Replacement Algorithms**: To efficiently manage which pages to swap in and out, the operating system uses page replacement algorithms such as Least Recently Used (LRU), First-In-First-Out (FIFO), and Optimal Page replacement. 3. **Thrashing**: If excessive paging occurs, the system may spend more time swapping pages in and out of the hard drive than executing actual processes. This condition is known as thrashing, which can significantly degrade system performance. The operating system must balance memory allocation to minimize thrashing. 4. **Memory Compression**: In some modern operating systems, memory compression is used as a technique to mitigate memory shortages. Compression reduces the amount of memory used by in-memory data, increasing the effective capacity of physical RAM. 5. **Dynamic Memory Allocation**: Operating systems dynamically allocate memory to applications as needed and reclaim it when it is no longer in use to optimize memory usage. Through these mechanisms, the operating system ensures that the limited physical memory resources are utilized efficiently, providing a seamless experience even when physical memory is constrained.
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