Virtual memory ppt
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briefly describe about virtual memory. what is virtual memory? advantage of virtual memory disadvantage of virtual memory needs of virtual memory LRU FIFO OPT FIFO ALGORITHM LRU ALGORITHM OPT ALGORITHM PAGE REPLACEMENT ALGORITHM
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Virtual memory
The document discusses the concept of virtual memory. Virtual memory allows a program to access more memory than what is physically available in RAM by storing unused portions of the program on disk. When a program requests data that is not currently in RAM, it triggers a page fault that causes the needed page to be swapped from disk into RAM. This allows the illusion of more memory than physically available through swapping pages between RAM and disk as needed by the program during execution.
Page replacement algorithms
This document discusses different page replacement algorithms used in operating systems. It begins by explaining the basic concept of page replacement that occurs when memory is full and a page fault happens. It then describes several common page replacement algorithms: FIFO, Optimal, LRU, LRU approximations using reference bits, and Second Chance. The key aspects of each algorithm are summarized, such as FIFO replacing the oldest page, Optimal replacing the page not used for longest time, and LRU approximating this by tracking recently used pages. The document provides an overview of page replacement techniques in computer systems.
Demand paging
Virtual Memory
• Copy-on-Write
• Page Replacement
• Allocation of Frames
• Thrashing
• Operating-System Examples
Background
Page Table When Some Pages Are Not in Main Memory
Steps in Handling a Page Fault
Virtual memory
Virtual memory is a technique that allows a program to use more memory than the amount physically installed on the system. When physical memory is full, infrequently used pages are written to disk. This allows processes with memory needs greater than physical memory to run. Common page replacement algorithms are first-in, first-out (FIFO), least recently used (LRU), and optimal (OPT) which replaces the page not used for the longest time. Virtual memory provides benefits like allowing more programs to run simultaneously but has disadvantages like reduced performance and system stability.
Page Replacement
Virtual memory management uses demand paging to load pages into memory only when needed. When memory is full and a new page is needed, a page must be replaced. Common replacement algorithms include FIFO, LRU, and Clock, with LRU and Clock approximating optimal replacement by selecting the least recently used page. Page buffering keeps replaced pages in memory briefly to avoid premature replacement.
Memory hierarchy
The document discusses the memory hierarchy in computers. It explains that main memory communicates directly with the CPU, while auxiliary memory devices like magnetic tapes and disks provide backup storage. The total memory is organized in a hierarchy from slow but high-capacity auxiliary devices to faster main memory to an even smaller and faster cache memory. The goal is to maximize access speed while minimizing costs. Cache memory helps speed access to frequently used data and programs.
Demand paging
n computer operating systems, demand paging is a method of virtual memory management. In a system that uses demand paging, the operating system copies a disk page into physical memory only if an attempt is made to access it and that page is not already in memory
Virtual memory presentation
Virtual memory allows a program to use more memory than the physical RAM installed on a computer. It works by storing portions of programs and data that are not actively being used on the hard disk, freeing up RAM for active portions. This gives the illusion to the user and programs that they have access to more memory than is physically present. Virtual memory provides advantages like allowing more programs to run at once and not requiring additional RAM purchases, but can reduce performance due to the need to access the hard disk.
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Virtual memory
The document discusses the concept of virtual memory. Virtual memory allows a program to access more memory than what is physically available in RAM by storing unused portions of the program on disk. When a program requests data that is not currently in RAM, it triggers a page fault that causes the needed page to be swapped from disk into RAM. This allows the illusion of more memory than physically available through swapping pages between RAM and disk as needed by the program during execution.
Page replacement algorithms
This document discusses different page replacement algorithms used in operating systems. It begins by explaining the basic concept of page replacement that occurs when memory is full and a page fault happens. It then describes several common page replacement algorithms: FIFO, Optimal, LRU, LRU approximations using reference bits, and Second Chance. The key aspects of each algorithm are summarized, such as FIFO replacing the oldest page, Optimal replacing the page not used for longest time, and LRU approximating this by tracking recently used pages. The document provides an overview of page replacement techniques in computer systems.
Demand paging
Virtual Memory
• Copy-on-Write
• Page Replacement
• Allocation of Frames
• Thrashing
• Operating-System Examples
Background
Page Table When Some Pages Are Not in Main Memory
Steps in Handling a Page Fault
Virtual memory
Virtual memory is a technique that allows a program to use more memory than the amount physically installed on the system. When physical memory is full, infrequently used pages are written to disk. This allows processes with memory needs greater than physical memory to run. Common page replacement algorithms are first-in, first-out (FIFO), least recently used (LRU), and optimal (OPT) which replaces the page not used for the longest time. Virtual memory provides benefits like allowing more programs to run simultaneously but has disadvantages like reduced performance and system stability.
Page Replacement
Virtual memory management uses demand paging to load pages into memory only when needed. When memory is full and a new page is needed, a page must be replaced. Common replacement algorithms include FIFO, LRU, and Clock, with LRU and Clock approximating optimal replacement by selecting the least recently used page. Page buffering keeps replaced pages in memory briefly to avoid premature replacement.
Memory hierarchy
The document discusses the memory hierarchy in computers. It explains that main memory communicates directly with the CPU, while auxiliary memory devices like magnetic tapes and disks provide backup storage. The total memory is organized in a hierarchy from slow but high-capacity auxiliary devices to faster main memory to an even smaller and faster cache memory. The goal is to maximize access speed while minimizing costs. Cache memory helps speed access to frequently used data and programs.
Demand paging
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Virtual memory presentation
Virtual memory allows a program to use more memory than the physical RAM installed on a computer. It works by storing portions of programs and data that are not actively being used on the hard disk, freeing up RAM for active portions. This gives the illusion to the user and programs that they have access to more memory than is physically present. Virtual memory provides advantages like allowing more programs to run at once and not requiring additional RAM purchases, but can reduce performance due to the need to access the hard disk.
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This document summarizes and compares paging and segmentation, two common memory management techniques. Paging divides physical memory into fixed-size frames and logical memory into same-sized pages. It maps pages to frames using a page table. Segmentation divides logical memory into variable-sized segments and uses a segment table to map segment numbers to physical addresses. Paging avoids external fragmentation but can cause internal fragmentation, while segmentation avoids internal fragmentation but can cause external fragmentation. Both approaches separate logical and physical address spaces but represent different models of how a process views memory.
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Memory organization (Computer architecture)
Memory is organized in a hierarchy with different levels providing trade-offs between speed and cost.
- Cache memory sits between the CPU and main memory for fastest access.
- Main memory (RAM) is where active programs and data reside and is faster than auxiliary memory but more expensive.
- Auxiliary memory (disks, tapes) provides backup storage and is slower than main memory but larger and cheaper.
Virtual memory manages this hierarchy through address translation techniques like paging that map virtual addresses to physical locations, allowing programs to access more memory than physically available. When data is needed from auxiliary memory a page fault occurs and page replacement algorithms determine what data to remove from main memory.
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Virtual memory allows a process's logical address space to be larger than physical memory by paging portions of memory to disk as needed. Demand paging brings pages into memory only when they are referenced, reducing I/O. When a page fault occurs and no frame is free, a page replacement algorithm like LRU selects a page to swap to disk. If processes continually page in and out without making progress, thrashing occurs, degrading performance. The working set model analyzes page references over a window to determine the minimum memory needed to avoid thrashing.
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In this paper I have described the memory management and allocation techniques in computer systems. The
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increasing throughput and processor utilization and by decreasing the response time and turnaround time.
Firstly I have compared Uniprogramming system with Multiprogramming system. After comparison I found
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memory utilization. Also the functionality of operating system routines which are responsible for user’s
memory partitioning must be improved to get better system performance in Multiprogramming system .In
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A REVIEW OF MEMORY ALLOCATION AND MANAGEMENT IN COMPUTER SYSTEMS
ABSTRACT :
In this paper I have described the memory management and allocation techniques in computer systems. The purpose of writing this survey paper is to elaborate the concept of memory allocation and management in computer systems because of the significance of memory component in computer system’s hardware. It is apparent from the work of computer scientists that effective and efficient main memory management and virtual memory management in computer systems improves the computer system’s performance by increasing throughput and processor utilization and by decreasing the response time and turnaround time. Firstly I have compared Uniprogramming system with Multiprogramming system. After comparison I found that Multiprogramming systems are quite better than Uniprogramming systems from the point of view of memory utilization. Also the functionality of operating system routines which are responsible for user’s memory partitioning must be improved to get better system performance in Multiprogramming system .In Uniprogramming system , the processor remains idle most of the time but dividing the memory into partitions for holding multiple processes as in Multiprogramming system does not solve the problem of idleness of a processor. Mostly all of the processes need I/O access, therefore processor also remain idle in Multiprogramming system. We have also discussed resource memory in detail and compared fixed partitioning with variable partitioning. After in depth study we found that variable partitioning is more advantageous than fixed partitioning because reallocation of page frames is impossible in fixed partitioning for a set of active processes at time instant‘t’. In this paper we have also discussed MIPS R2/3000 machine virtual to real address mapping in detail so that virtual to real address mapping can be understood through a machine’s architecture and example.
KEYWORDS:
Queues, Long Term Queues, Short Term Queues, I/O Queues, Swapping, Processor Scheduling, Fixed Partitioning, Variable Partitioning, Page Frames, Pages, Virtual Memory, Physical Memory, Processor Utilization, Throughput, Response Time, Turnaround Time
VIEW OF MEMORY ALLOCATION AND MANAGEMENT IN COMPUTER SYSTEMS
This document summarizes memory allocation and management techniques in computer systems. It compares uniprogramming and multiprogramming systems, discussing how multiprogramming improves processor utilization by allowing multiple processes to occupy memory simultaneously. It describes different types of queues used in memory and processor scheduling. It also discusses fixed and variable partitioning for allocating memory to processes, noting variable partitioning is more advantageous as it allows reallocating memory. Finally, it provides an example of virtual to physical address mapping in MIPS R2/3000 architecture.
6416cseij01
This document summarizes memory allocation and management techniques in computer systems. It compares uniprogramming and multiprogramming systems, discussing how multiprogramming improves processor utilization by allowing multiple processes to occupy memory simultaneously. It describes different types of queues used in memory and processor scheduling. It also discusses fixed and variable partitioning for allocating memory to processes, noting variable partitioning is more advantageous as it allows reallocating memory. Finally, it provides an example of virtual to physical address mapping in MIPS R2/3000 architecture.
Virtual memory ppts
Virtual memory is a technique that allows for more memory to be available to programs than the physical memory installed on the computer. When physical memory is full, infrequently used memory pages are written to secondary storage like a hard disk. This allows processes to access more memory than is physically available. Page replacement algorithms like FIFO, LRU, and OPT are used to determine which memory pages should be removed from physical memory and written to secondary storage when space is needed. Virtual memory provides advantages like allowing processes to exceed physical memory limits and improving performance when only parts of programs are actively being used. However, it can reduce performance and system stability when disk access is frequently required.
Paging +Algorithem+Segmentation+memory management
The document discusses memory management techniques used in computer systems, including memory partitioning, paging, segmentation, and virtual memory. It provides details on:
1) How memory is divided between the operating system and currently running program.
2) The use of fixed and variable size partitions and their tradeoffs.
3) How paging divides programs and memory into pages to more efficiently allocate memory.
4) How segmentation further subdivides memory to simplify programming and enable access controls.
5) How virtual memory uses paging, disk storage, and demand paging to make programs appear larger than physical memory.
Similar to Virtual memory ppt (20)
A Review of Memory Allocation and Management in Computer Systems
A Review of Memory Allocation and Management in Computer Systems
Computer Science & Engineering: An International Journal (CSEIJ)
Computer Science & Engineering: An International Journal (CSEIJ)
A REVIEW OF MEMORY ALLOCATION AND MANAGEMENT IN COMPUTER SYSTEMS
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VIEW OF MEMORY ALLOCATION AND MANAGEMENT IN COMPUTER SYSTEMS
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Virtual memory ppt
- 1. Present by :- Ritul De
- 2. CONTENTS Introduction Advantages of Virtual Memory Disadvantage ofVirtual Memory FIFO LRU Page Replacement Algorithms OPT
- 3. Introduction Virtual memory is a separation of user logical memory from physical memory. In this method, we keep only a part of the process in the memory and other part on the disk (secondary storage)
- 4. Only part of the program needs to be in memory for execution. Logical address space is much larger than physical address space. Need to allow pages to be swapped in and out. Virtual memory allows speed gain when only a particular segment of the program is required for the execution of the program. This concept is very helpful in implementing multiprogramming environment.
- 5. Applications run slower if the system is using virtual memory. ItTakes more time to switch between applications. Less hard drive space for your use. It reduces system stability.
- 6. It is the technique used by operating system to decide which memory pages swap out . It is also decided that is memory , how much frames to allocate to each process.
- 7. First In First Out (FIFO) Algorithm Very simple to implement Oldest page is replaced for replacement Performance is not always good 1 2 3 4 2 3 4 1 3 4 1 2 5 1 2 5 3 2 5 3 4 4 1 2 5 3 4
- 8. Page which has not been used for the longest time in main memory the one which will be selected for replacement. It is like optimal page-replacement algorithm looking backwards in time. 7 0 1 2 0 1 2 0 3 4 0 3 4 0 2 4 3 2 2 4 2 3
- 9. Looks for page in future Lowest page fault Difficult to implement 7 0 1 2 0 1 7 0 1 2 0 1 2 0 3 2 0 3 2 4 3 2 3 4 0 1 7