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Chapter 13 Address Space. Chien -Chung Shen CIS, UD [email protected] Lack of M emory Abstraction. Earlier systems did not provide much of an abstraction of (physical) memory OS == library that sat in memory starting from physical address 0

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Chapter 13 address space

Chapter 13Address Space

Chien-Chung Shen

CIS, UD

[email protected]


Lack of m emory abstraction
Lack of Memory Abstraction

  • Earlier systems did not provide much of an abstraction of (physical) memory

    • OS == library that sat in memory starting from physical address 0

    • One running program that sat in memory starting from physical address 64K


Multiprogramming
Multiprogramming

  • Multiple concurrent processes

    • increase utilization

    • time sharing & interactive

  • Leave processes in memory and switch between them

  • One critical issue

    • protection


Address space
Address Space

  • Abstractionof physical memory

    • Running program’s view of physical memory: contain all the memory state of running program

    • The process is NOT in memory at physical addresses 0 through 16KB

    • Virtual address vs. physical address

  • Address spaces of threads ?

  • How to virtualize memory ?

    • How can the OS build this abstraction of a private, potentially large address space for multiple running processes (all sharing memory) on top of a single, physical memory?


Goals
Goals

  • Transparency

    • virtualized memory is implemented in a way that is invisible to the running program

    • program behaves as if it has its own private physical memory

    • OS and hardware do all the work to multiplex memory among many different processes, and hence implement the illusion

  • Efficiency – time and space

  • Protection

    • isolation – microkernel walls off pieces of the OS from other pieces of the OS


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