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

Ceng 334 - Operating Systems 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

Ceng 334 - Operating Systems 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

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

Ceng 334 - Operating Systems

Ceng 334 - Operating Systems 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

Ceng 334 - Operating Systems

Ceng 334 - Operating Systems 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

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

Ceng 334 - Operating Systems

Ceng 334 - Operating Systems

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

Ceng 334 - Operating Systems 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

Ceng 334 - Operating Systems 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

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

Ceng 334 - Operating Systems 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

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

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

Ceng 334 - Operating Systems 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

Ceng 334 - Operating Systems 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

Ceng 334 - Operating Systems 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

Ceng 334 - Operating Systems 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

Ceng 334 - Operating Systems

Comparative OS Characteristics Ceng 334 - Operating Systems

Ceng 334 - Operating Systems 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