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Operating Systems Design (CS 423)

Operating Systems Design (CS 423). Elsa L Gunter 2112 SC, UIUC http://www.cs.illinois.edu/class/cs423/. Based on slides by Roy Campbell, Sam King, and Andrew S Tanenbaum. I/O Software: Principles. Device independence

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Operating Systems Design (CS 423)

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  1. Operating Systems Design (CS 423) Elsa L Gunter 2112 SC, UIUC http://www.cs.illinois.edu/class/cs423/ Based on slides by Roy Campbell, Sam King, and Andrew S Tanenbaum

  2. I/O Software: Principles • Device independence • Possible to write programs that can access any Io device without having to specify device in advance • Read file as input on a floppy, hard disk, or CD‐ROM, without modifying program for each device

  3. I/O Software: Principles • Uniform naming • Name of file or device should simply be a string or an integer and not depend on device in anyway • Example: Plan9 • All drivers are files in file system name space

  4. I/O Software: Principles • Buffering • Systems are busy, devices have limited storage • Keep extra data in software to make device appear to have more space • Example: Network packets, audio

  5. I/O Software: Principles • Shared vs dedicated devices: • Allowing for sharing, considering two user sharing open files • Example: Disk, audio devices • Often sharing supported in libraries

  6. Device drivers in VMMs • Problem: multiple OSes all expecting exclusive access to the underlying hardware • Solution: another layer of software

  7. Devices in VMMs • Physical reality: • Single set of real hardware • Shared among multiple OSes, possibly wanting different hardware • Illusion: • Each OS gets sole use of its own specific (virtual) hardware • Solution: • Software version of real hardware

  8. Virtual Devices Guest Software(OS) Dev Drv VMM Virt Dev

  9. Type I VMM Guest Software(OS) Guest Software(OS) Dev Drv Dev Drv VMM Virt Dev Virt Dev Real Dev Driver Hardware Real Device

  10. Type II VMM Guest Software(OS) Guest Software(OS) Dev Drv Dev Drv VMM Virt Dev Virt Dev Host OS Real Dev Driver Hardware Real Device

  11. Type I/II VMM Hybrib Guest Software(OS) VMM App Dev Drv Host OS VMM Virt Dev VMM Real Dev Dvr Hardware Real Dev Real Dev Driver Real Device

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