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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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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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