Memory Management in Operating System (English) скачать в хорошем качестве

Memory Management in Operating System (English)

Memory Management Study Guide This guide provides a comprehensive review of key concepts in operating system memory management, based on the provided source materials. It includes a short-answer quiz, an answer key, suggested essay questions for deeper study, and a complete glossary of terms. Quiz Answer the following ten questions in 2-3 sentences each to test your understanding of the core concepts. 1. What are the three most important criteria for memory, and what hierarchical structure is used to balance these criteria? 2. Explain the difference between a Logical Address and a Physical Address. 3. Describe the two types of memory fragmentation and how they differ. 4. What is the "Best-Fit" allocation strategy, and what is a major disadvantage of this approach? 5. Define "compaction" and explain its primary purpose in memory management. 6. In the context of paging, what are "pages" and "frames," and what is their relationship? 7. What is a Translation Look-aside Buffer (TLB), and how does it address the performance issues of storing page tables in main memory? 8. How does Segmentation support the "user view of memory" in a way that Paging does not? 9. Explain the concept of Demand Paging and identify one of its main benefits. 10. Define "thrashing" and explain why it leads to low CPU utilization. Answer Key 1. The three important criteria for memory are Size, Access Time, and Per-unit Cost. To achieve a balance of these criteria, a memory hierarchy is used, which typically consists of the CPU Cache, Main Memory, and Disk, organized from fastest and most expensive to slowest and least expensive. 2. A Logical Address, also known as a virtual address, is generated by the CPU. A Physical Address is the address seen by the memory unit itself. The concept of binding a logical address space to a separate physical address space is central to memory management. 3. Internal Fragmentation arises when the memory allocated to a process is larger than the process itself, leading to unused space within the allocated partition. External Fragmentation occurs when free memory areas exist but are too small and non-contiguous to be allocated to a new process that needs a larger, single block of memory. 4. The "Best-Fit" strategy allocates a process to the smallest available free partition that is large enough to hold it. A major disadvantage is that it tends to produce many uselessly tiny free fragments, is slow in both allocation and deallocation, and still suffers from internal fragmentation. 5. Compaction is a technique used to avoid external fragmentation by moving all running processes toward one end of memory. This consolidates all the small, free memory blocks into a single large, contiguous block. 6. In paging, logical memory is divided into fixed-size blocks called pages. Physical memory is divided into blocks of the same size called frames. To run a program, its pages are loaded into available frames in physical memory, which do not need to be contiguous. 7. A Translation Look-aside Buffer (TLB) is a special, small, fast-lookup hardware cache that stores a few of the most recently used page-table entries (mapping page numbers to frame numbers). It solves the performance problem of requiring two memory accesses (one for the page table, one for the data) by providing a much faster way to find the frame number for a logical address. 8. Segmentation supports the user's view of memory because it divides a program into logical units of varying sizes, such as a main program, functions, and data structures. In contrast, Paging divides a program into arbitrary, fixed-size pages, which does not preserve the logical structure of the program from the user's perspective. 9. Demand Paging is a virtual memory technique where a page is brought into main memory only when it is needed. A key benefit is that it requires less memory to run a program, which leads to a faster response time and allows more users to be supported on the system. 10. Thrashing is a state where a process is spending more time swapping pages in and out of memory than executing. It occurs when a process does not have enough pages in memory to accommodate its "working set," leading to a high page-fault rate and, consequently, low CPU utilization as the system is preoccupied with I/O for paging.