39 virtual memory
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Virtual memory allows treating main memory as a cache for pages on disk. It implements the separation of user logical memory from physical memory, allowing logical address spaces to be much larger than physical memory. Virtual memory can be implemented via demand paging or demand segmentation and gives advantages like higher multiprogramming and allowing very large logical address spaces by paging pages between disk and memory as needed.
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a glance on memory management in operating system.
this note is useful for those who are keen to know about how the OS works and a brief explanation regarding several terms such
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segmentation
fragmentation
virtual memory
page table
to A Level A2 Computing students, this light note may be helpful for your revision
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Virtual memory allows programs to be larger than physical RAM by storing parts of programs and data on disk when not actively being used. This allows multiple programs to share limited RAM, improving CPU and disk utilization. The OS manages mapping between logical memory addresses seen by programs and physical addresses in RAM through a memory management unit. Virtual memory frees programmers from worrying about physical memory limitations and improves performance by reducing disk I/O for memory swapping.
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This document provides an overview of memory management techniques in operating systems, including both static and dynamic allocation approaches. It discusses fixed and variable partitioning for static allocation, as well as first-fit, next-fit, best-fit, and worst-fit algorithms for dynamic allocation. The document also covers fragmentation, base-limit registers, swapping, paging, and segmentation for virtual memory management. The key aspects of paging include using page tables to map virtual to physical addresses, allowing sharing and abstracting physical organization. Segmentation divides memory into logical segments specified by segment tables.
Writing Scalable Software in Java
Writing Scalable Software in Java - From multi-core to grid-computing
Virtual memory
Virtual memory allows programs to access more memory than the physical memory available on a computer by storing unused portions of memory on disk. It was first developed in 1959-1962 at the University of Manchester. Key aspects of virtual memory include: dividing memory into pages that can be swapped between disk and physical memory as needed, using page tables to map virtual to physical addresses, and page replacement algorithms like LRU to determine which pages to swap out. Virtual memory provides benefits like running more programs simultaneously but can reduce performance due to disk access times.
The life and times
Virtual memory is a memory management technique that uses secondary storage like hard disks to simulate a larger main memory for a process. It allows processes to have a larger address space than the actual physical memory size by swapping pages between main memory and secondary storage. This helps simplify memory management, protect processes from each other, and allows the operating system to share main memory among multiple processes. Virtual memory uses a memory hierarchy with different storage levels having varying sizes and speeds, and implements paging to map virtual addresses to physical addresses through page tables.
Csc1401 lecture05 - cache memory
The document discusses cache memory principles and design. It begins with an overview of the memory hierarchy and how cache memory fits between the CPU and main memory. It then covers key elements of cache design, including cache addressing, size, mapping functions, and replacement algorithms. Mapping functions discussed include direct mapping, associative mapping, and set associative mapping. The document provides examples and diagrams to illustrate these cache mapping techniques.
Caching principles-solutions
This document provides an overview of caching and distributed caching principles. It discusses the goals of caching to improve performance by storing frequently accessed data closer to where it is needed. It explains concepts like memory hierarchy and why distributed caching is needed to manage huge amounts of data across multiple servers. Some key use cases of caching are also mentioned. The document discusses caching topologies like partitioned and replicated caching. It provides examples of caching patterns and load techniques. Finally, it discusses some prominent distributed caching solutions and shows sample code for using Hazelcast.
32 dynamic linking nd overlays
Dynamic linking and overlays are techniques for improving memory utilization in operating systems. Dynamic linking postpones linking of library routines until execution using stubs. This allows better memory usage and automatic use of new library versions. Overlays improve memory usage for large programs by loading only required parts into memory at a given time using an overlay manager. Both have advantages of improved memory usage but overlays require complex programming and are slower.
Cache memory and virtual memory
This document discusses cache memory and virtual memory. It defines cache memory as fast memory that acts as a buffer between the CPU and RAM, holding frequently used data and instructions. It also describes how cache memory works to reduce average memory access time. Virtual memory is defined as a technique where secondary memory is used like primary memory. It discusses how virtual memory uses pages and page tables to map virtual memory addresses to physical memory locations, transferring pages between RAM and disk as needed. The document provides information on types of cache memory, applications of cache memory, and types and applications of virtual memory.
Virtual memory managment
Virtual memory allows programs to access memory beyond the available physical memory by storing inactive memory pages on disk. This separation of physical and virtual memory makes programming easier and allows memory to be shared between processes. When a program requests a page not in memory, demand paging loads it from disk. If no frames are available, page replacement writes the contents of an unused frame to disk to free it for the requested page. Thrashing occurs when too many pages are continuously replaced from disk due to insufficient memory, degrading system performance.
Memory Management
This document discusses memory management techniques used in computer systems. It covers five key requirements of memory management: relocation, protection, sharing, logical organization, and physical organization. It then describes approaches to memory management like fixed partitioning, placement algorithms, relocation, virtual memory, paging, and the use of page tables to translate virtual addresses to physical addresses. The goal is to efficiently manage the limited main memory and allow multiple processes to efficiently share memory.
Time For DIME
Data In Memory Exploitation (DIME) presentation. Given UKCMG Annual Conference May 2013 and System z Technical University June 2013
Hyper-V Dynamic Memory in Depth
Hyper-V Dynamic Memory allows virtual machines to dynamically adjust their memory usage. It uses techniques like ballooning and external page sharing to optimize memory allocation. The goal is to improve consolidation ratios with minimal performance impact. Dynamic Memory treats memory as a dynamically schedulable resource like CPU. It adds memory to VMs when needed and reclaims unused memory periodically to improve overall utilization.
Lect13
The document discusses different techniques for managing memory in operating systems, including fixed and dynamic partitioning, paging, segmentation, and swapping, which allows processes to be swapped temporarily to disk to improve memory utilization and enable more processes to run simultaneously than can fit in physical memory. Memory management aims to allocate memory efficiently while supporting protection between processes and relocation of processes in memory.
Lect13
The document discusses memory management in operating systems. It describes how operating systems allocate memory to processes and track which memory is in use and which is free. It discusses different memory management techniques including fixed partitions, dynamic partitioning with variable sized partitions, and compaction to reduce fragmentation. It also summarizes different dynamic partitioning placement algorithms like first-fit, next-fit, best-fit, and worst-fit.
Cache memory presentation
Cache is a small amount of fast memory located close to the CPU that stores frequently accessed instructions and data. It speeds up processing by allowing the CPU to access needed information more quickly than from main memory. Caches exploit the principle of locality of reference, where programs tend to access the same data/instructions repeatedly over short periods. There are multiple cache levels, with L1 cache being fastest but smallest and L3 cache being largest but slower. Caching improves performance dramatically by fulfilling over 90% of memory requests from the small cache rather than requiring slower access to main memory.
Memory management
This document discusses memory management in operating systems. It defines memory management as allocating RAM to user programs and reclaiming memory after programs finish. It also describes protecting each user's memory from other programs. The document discusses physical and virtual memory, and types of virtual memory including paged, segmented, and swapped memory. It defines static and dynamic memory allocation, with static allocation assigning fixed memory at compile time and dynamic allocation assigning variable memory as needed from the heap.
Week 4Operating SystemsCardPunch - verif.docx
Week 4
Operating Systems
Card
Punch - verify - sort - process - print - archive
Batch – static – rigid - time intensive - manual – automate sequential vs random
memory constraints
Smart IO, CU, width
CU – offload work – CPU -GPU
Benchmark – Clock Speed – Overclocking
Bigger is better – more instructions – memory – colors – IO devices – IP addresses – yada yada -
Mono Processing - Program application owns all HW resources
OpCode ---- Operand (parameters)
Von Neumann – function – structure
Week 4Program set of instructionsProcess / task program in executionEach process has it’s own address spaceConsisting of instruction region Data regionStack region Process run for an interval or quantum of time
Uni-programmingDifficult application developmentAssembler or machine languageNo error recoveryJob scheduling (batch processing)Processor had to do all operations Inefficient use of resourcesNon real-time
Operating SystemDefinition “software that controls hardware”Resource manager - GatekeeperInterface between user and hardwareSeparates application from hardwareFile managerKernel is the core component of the OS
OS
Single-user, dedicated machine
User program
Unused
Memory
OS Objectives and FunctionsConvenienceMaking the computer easier to useEfficiencyAllowing better use of computer resourcesSimplicity Application developers can use system procedures to reduce code
*
MultiprogrammingCarve memory into partitionsUnique app’s loaded into each partitionOperating system switches HW resources between partitions for a quantum of timeAppears to run simultaneouslyEfficient use of processor resourcesReal-time dataCon = overhead, complex
Partition 1
Partition 2
Partition 3
Operating System
Hardware
Time a
Time b
Time c
Application a
Application b
Application c
M
E
M
O
R
Y
M
E
M
O
R
Y
Process statesRunningReadyBlockedWaitSuspended
Scheduling AlgorithmsFirst-In-First-Out FIFORound-Robin RRShortest-Process-First SPFShortest-Remaining-Time SRTMultilevel Feedback QueueFair Share Scheduling
FIFO
CPU
A
B
C
Completion
Job Queue
A
Preemption
RR
Process control blockPID- Process identification numberPC- Program counterRegistersStatePriorityAddress spaceFlags / etc
Multitasking
Layers and Views of a Computer System
*
Operating System ServicesProgram creationProgram executionAccess to I/O devicesControlled access to filesSystem accessError detection and responseAccounting
*
O/S as a Resource Manager
*
Memory managementFixed size partitioningVariable-size partitioningFragmentationMemory leak
Fixed size partitioning
Variable-size partitioning
Issues with address space - Fragmentation
Memory Leak
4K Page Segment
4K Page Segment
4K Page Segment
4K Page Segment
Disk
Memory
Fr.
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39 virtual memory
- 1. Storage Management • Virtual Memory 1
- 2. HOME PREVIOUS TOPIC NEXT PREVIOUS QUESTION PAPERS FOR OS CPP TUTORIALS 9CM402.39 2
- 3. Recap In the last class, you have learnt: • Paged Segmentation • MULTICS Address Translation Scheme 3
- 4. Objective On completion of this class, you will be able to know • Virtual Memory Techniques 4
- 5. Virtual Memory Techniques • RAM is expensive ( but fast ), disk is cheap (but slow) • Need to find a way to use the cheaper memory – Store memory that isn’t frequently used on disk – Swap pages between disk and memory as needed • Treat main memory as a cache for pages on disk 5
- 6. Virtual Memory • It is separation of user logical memory from physical memory – Only part of the program needs to be in memory for execution – Logical address space can therefore be much larger than physical address space – Allows address spaces to be shared by several processes – Allows for more efficient process creation 6
- 7. Virtual Memory • Virtual memory can be implemented via: – Demand paging – Demand segmentation 7
- 8. Virtual Memory • It is a conceptual separation of user logical memory from physical memory • Thus we can have large virtual memory on a small physical memory Individual Pages Physical Disk Virtual Memory Memory Map Memory 8
- 9. Virtual Memory • Programs can be larger than memory – Program loaded into memory as needed – Active program and data “swapped” to a disk until needed • Memory space treated uniformly 9
- 10. WHY VIRTUAL MEMORY? • Previously entire logical space was required for the process to be in memory • Before the process could run • The alternatives to this • Most code / data isn't needed at any instant, or even within a finite time • We can bring it in only as needed 10
- 11. Virtual Memory Advantages • Gives a higher level of multiprogramming • The program size isn't constrained (thus the term 'virtual memory'). Virtual memory allows very large logical address spaces • Swap sizes smaller 11
- 12. Summary In this class, you have learnt • Virtual Memory 12
- 13. Frequently Asked Questions • Explain Virtual Memory concepts with a neat sketch 13
- 14. Quiz 1. __________separation of user logical memory from physical memory a) Segmentation b) Virtual memory c) None 2. ____________gives a higher level of multiprogramming a) Page offset b) Hole c) Virtual memory d) None 14
- 15. Quiz 3. Logical address space can be much larger than a) Page number b) MULTICS c) Physical address space d) None 4. __________allows very large logical address spaces a) External fragmentation b) Virtual memory c) Compaction d) None 15
- 16. Other subject materials • Web designing • Micro processors • C++ tutorials • java home