Operating System - memory Management Part 4 - Notes, Study notes of Operating Systems

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MEMORY MANAGEMENT

Shared Pages

Example

User’s

View of a

Program

Logical View of Segmentation

1 4 2 3 user space physical memory space

Virtual Memory

• (^) Background
• (^) Demand Paging
• (^) Process Creation
• (^) Page Replacement
• (^) Allocation of Frames
• (^) Thrashing
• (^) Demand Segmentation
• (^) Operating System Examples

Definition: Virtual Memory

• (^) Virtual Memory is a memory management technique that allows execution of a program that is not completely in memory.
• (^) Virtual memory considers main memory as extremely large uniform array of storage.
• (^) Virtual memory provides separation of user logical memory from physical memory.

Background

• (^) As we know that instructions being executed must be in the main memory.
• (^) This needs to place entire logical memory into the main memory.
• (^) Under this consideration we can only execute a program of maximum size requirement is equal to main memory.

Background

• (^) It is not important to load complete program to main memory because - (^) Error handling codes executes occasionally. - (^) Some of the functions are rarely used. - (^) Some Data Structures reserve more memory space than their actual requirement.
• (^) This suggests that the ability to store program partially would have many benefits.

Advantages of Virtual Memory

• (^) Availability of multiple program in main memory will increase degree of multi-programability , throughput and CPU utilization.
• (^) If multiple programs are running together, less input output is required from users side.

Working of Virtual Memory

• (^) A program can be handled by users perspective without knowing anything about physical memory.
• (^) It is possible to provide extremely large virtual memory when a limited physical memory is present there.

Virtual-address Space

• (^) The virtual address space of a process refers to the logical or virtual view of how a process is stored in the main memory.

Virtual-address Space

• (^) Here we allow the heap to grow upwards in memory as it uses dynamic memory allocation.
• (^) Stack is growing downwards through successive function calls.
• (^) Besides this sparse address space is available to serve the growing requirements.

Shared Library

Using Virtual

Memory

Implementation of Virtual

Memory

• (^) Virtual memory can be implemented via:
  • (^) Demand paging
  • (^) Demand segmentation