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OS Structures

OS Structures. Agenda. OS design and implementation Simple structure 3. Layered structure Microkernels Modular structure. 1. OS design and implementation. An art of balance hardware vs software efficiency vs flexibility user vs system convenience vs effectiveness

clementine-skinner
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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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