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Chapter 6 : Case Studies

Chapter 6 : Case Studies. UNIX Dos Windows 95 Windows NT. UNIX. There are two main versions: AT&T System V Release 4 (SVR4) Originally developed by AT&T, now SCO BSD (Berkeley Software Distribution). Supports various architectures Structure varies Supports preemptive multitasking

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Chapter 6 : Case Studies

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  1. Chapter 6 : Case Studies • UNIX • Dos • Windows 95 • Windows NT Ceng 334 - Operating Systems

  2. UNIX • There are two main versions: • AT&T System V Release 4 (SVR4) • Originally developed by AT&T, now SCO • BSD (Berkeley Software Distribution) Ceng 334 - Operating Systems

  3. Supports various architectures • Structure varies • Supports preemptive multitasking • Multiuser environment - generally secure • Supports multithreaded applications • Protection/Security is high on modern versions Ceng 334 - Operating Systems

  4. Supports symmetric multiprocessing • Highly scalabe/portable to various systems • Many types/flavours of UNIX exist Ceng 334 - Operating Systems

  5. Ceng 334 - Operating Systems

  6. MS-DOS • Limited to x86 architecture • Simple Structure • Single User (No tasking, scheduling, priorities) • No protection • Monolithic structure • Old, outdated but still widely used (hardware and cost driven decision) Ceng 334 - Operating Systems

  7. Ceng 334 - Operating Systems

  8. Windows 95 • x86 architecture • Layered • Single user • 32 bit applications run in a preemptive, multithreaded, multitasking environment • 16 bit applications (of Windows 3.x) run in shared memory space in a cooperative multitasking environment Ceng 334 - Operating Systems

  9. Virtual DOS Machine for DOS applications • “Plug and Play” - new OS “advantage” Ceng 334 - Operating Systems

  10. Ceng 334 - Operating Systems

  11. Ceng 334 - Operating Systems

  12. System Virtual Machine DOS Virtual Machines DOS app Win32 app System services, KERNEL, USER, and GDI Win16 app DOS app Win32 app Win16 app DOS app Win32 app Ring 3 Virtual Machine Manager subsystem File Management subsystem Ring 0 Windows 95 Architecture Ceng 334 - Operating Systems

  13. VMM (Virtual Machine Manager) and file management subsystems run in ring 0 (the most privileged level of the four-ring Intel 386 protection model). This implies these two modules have unrestricted access to the whole system. • VMM provides memory management, scheduling and DOS Protected Mode Interface (DPMI) • VMM also includes all Virtual Extended Drivers (VxDs) to virtualize hardware devices. Ceng 334 - Operating Systems

  14. The system Virtual Machine runs in ring 3 (The only other protection level used by Win 95. Ring 3 is the least privileged, best isolated level) • All applications and core dynamic link libraries (DLLs) - KERNEL, USER, and GDI execute in the VM Ceng 334 - Operating Systems

  15. Multitasking & Multithreading • Multiple concurrent threads • Time is allocated on a per-thread basis • DOS VMs and VM address space shared by Win16 applications constitute one thread each • Each Win32 apps represent at least one, and possibly two or more, threads Ceng 334 - Operating Systems

  16. Scheduling • The scheduler allocates time based on execution priority, taking into account factors such as whether the thread belongs to a foreground or background process and how long it has been since the thread was last run • Win32 and DOS apps are preemptively multitasked. • Win16 apps are cooperatively multitasked within the time slice allocated. Ceng 334 - Operating Systems

  17. Desynchronized Input Queues • An input queue is where hardware generated messages such as mouse clicks and keystrokes are stored for app retrieveal • Win95 assigns each application its own input queue • In Windows 3.x there is only one input queue so a misbehaving process may delay all other applications Ceng 334 - Operating Systems

  18. (Symmetric Multiprocessing) SMP • Not applicable to Win95. • Only in NT versions Ceng 334 - Operating Systems

  19. File System • Windows 3.x Oss use DOS services to perform file I/O. • Win95 uses a 32-bit (16-bit for Windows 3.x) file system VFAT (Virtual FAT) • VFAT is compatible with FAT volumes • VFAT permits long file names (up to 255 characters) Ceng 334 - Operating Systems

  20. Windows NT • 32 bit preemptive multitasking OS • Supports different chip architectures (CISC and RISC) • Can work as a server or client (workstation) • Has the same GUI as Windows 95 • Modular style • Multiuser, multitasking • Supports threads as well as classical processes Ceng 334 - Operating Systems

  21. Support SMP (Symmetric Multiprocessing) (1 to 32 processors) • Designed with security in mind • Supports distributed processing - networking is a core component to the OS • Supports RPCs • Very robust (reliable) Ceng 334 - Operating Systems

  22. The HAL (Hardware Abstraction Level) makes porting very easy • Supports non-NT applications through environment sub systems - meaning it can run Win32, OS/2 and POSIX applications (supports multiple personalities) • NT style OSes are the way of the future Ceng 334 - Operating Systems

  23. Ceng 334 - Operating Systems

  24. Comparative OS Characteristics Ceng 334 - Operating Systems

  25. References • Modern Operating Systems, Andrew S. Tanenbaum, Prentice-Hall, 1992 • Operating Systems (Second Edition), William Stallings, Prentice-Hall, 1995 • Local Area Networks : A Client/Server Approach, James E. Goldman, John Wiley&Sons, 1997 • Your Next Operating System, PC Magazine, September 26, 1995, pp. 102-159 • Windows 95 And Its Competitors, PC Magazine, May 16, 1995, pp. 139-156 • Chicago: Under Construction, PC Magazine, April 12, 1994, pp. 183-207 Ceng 334 - Operating Systems

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