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OS Structures

This overview explores various operating system structures including simple, layered, microkernel, and modular designs. It highlights the merits and challenges of each architecture, such as MS-DOS’s simplistic single-user approach versus more complex layered systems like Unix. The microkernel design minimizes kernel responsibilities, emphasizing modularity and the message-passing model for communication. Additionally, the document covers general design guidelines and modern practices in operating system design, making it a valuable resource for understanding the art of OS balance between efficiency, flexibility, and user needs.

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OS Structures

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  1. OS Structures

  2. Agenda • OS design and implementation • Simple structure • 3. Layered structure • Microkernels • Modular structure

  3. 1. OS design and implementation • An art of balance • hardware vs software • efficiency vs flexibility • user vs system • convenience vs effectiveness • General design guidelines • separation of mechanisms and policies • Best current practices CSc 360Overview

  4. 2. Simple Structure (1) • E.g., MS-DOS • single user • almost single process • direct access • almost flat memory • MZ linked list • executables • .COM: segment limit • .EXE: MZ file magic CSc 360Overview

  5. 2. Simple structure (2) MS-DOS • Load program • “shrink” interpreter • make room for program • Execute program • access to everywhere • even “kernel”/interpreter • Reload interpreter back • otherwise, “cannot find command.com…” CSc 360Overview

  6. 3. Layered structure (1) • Layers • L0: hardware • LN: user interface • Li: anything in btw • use Li-1 service • offer service to Li+1 • Divide & conquer • Cross-layer issues CSc 360Overview

  7. 3. Layered structure (2) Unix • Hybrid structure CSc 360Overview

  8. 4. Micro-kernel structure • E.g. • Mach • Smaller kernel • only those “essentials” • e.g., handle hardware • More by system/application programs • message passing • Overhead between kernel and user spaces file client file server kernel CSc 360Overview

  9. 5. Modular structure (1) • Object-oriented methodology • not necessary implemented in OO languages • popular choices for modern OS, e.g., Linux • e.g., insmod fat|vfat|msdos • On-demand, loadable kernel modules • each module is a separate function/support • communicate through know kernel interface • module dependency CSc 360Overview

  10. 5. Modular structure (2): Mac OS X • Mach (CPU,memory) + BSD (file,network) CSc 360Overview

  11. 5. Modular structure (3): SunOS Solaris • Modular design (high-level diagram) CSc 360Overview

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