Windows 2000

1. Windows 2000 Michael BlinnBen HejlJane McHughMatthew VanMater

2. Overview • Environment • Designed to provide a true 32-bit, preemptive, reentrant, virtual memory OS • Run on multiple hardware architectures and platforms • Run and scale well on SMP systems • Network client and server • Run most existing 16-bit MD-DOS and Microsoft Windows 3.1 applications • Supports Unicode • Portable through the use of Hardware Abstraction Layer (HAL)

3. Overview Continued • Uses some state-of-the-art concepts. • Object Oriented design • Hybrid Microkernel • As of February 2001, over one million licenses for the Server have been sold.

4. Overview Continued • Strengths • Hybrid Microkernel • APIs • Allow compatibility • Weaknesses • Weak remote administration facilities

5. Scheduling • Priorities • Levels • 32 priority levels, ranging from 0 to 31. • Each process has one priority level, threads have two • Queues and Data Structures • Series of queues- one for each scheduling priority • Queues contain threads that are in the ready state • Ready summary bitmask • Idle summary bitmask

6. Scheduling Continued • Queues and Data Structures Continued • Wait queues handled differently • Current priority threads can be boosted • Upon completion of an I/O operation • After waiting on executive events or semaphores • After threads in the foreground process complete a wait operation • When GUI threads wake up • When a thread that is ready to run has been waiting for some time

7. Scheduling Continued • I/O requests to devices that warrant better responsiveness have higher boost values. • After the boost is applied, the thread is ran for one quantum at the elevated priority level, after which it decays one priority level, and so on. • CPU Starvation • Win2K maintains a system thread called the balance set manager.

8. Scheduling Continued • Real Time • 15 priority levels in Windows 2000 • Levels normally reserved for kernel-mode system threads. • Win2K does not provide real-time operating system facilities.

9. Scheduling Continued • Priority Scheduling Differences in a Multi-Processor Environment • Steps after a thread is selected for execution • Schedule the thread on an idle processor in order of ideal, last, and current CPU. • Schedule the thread on any idle processor. • Preempt a thread currently running on a processor in order of ideal, last, and current CPU.

10. Scheduling Continued • Thread States • Ready- thread waiting to execute • Standby- thread selected to run next • Running- executing thread • Waiting- thread waiting on an event to occur • Transition- thread ready but paged out of memory • Terminated- thread that finishes execution • Initialized- used when a thread is being created

11. Scheduling Continued • Thread Transitions • Voluntary Switch • Preemption • Quantum end • Termination

12. Scheduling Continued • The Zero Page Thread • Enables and disables interrupts • Checks for any DPCs pending on any processor and delivers them if necessary • Checks whether a thread has been selected to run next on the CPU and, if so, dispatches it • Performs checks for power management functions

13. Scheduling Continued • In Win2K, a thread’s context and the procedure for context switching vary depending on the processor’s architecture. • Saving and reloading of this data is made possible by using a kernel-mode stack.

14. Scheduling Continued • Typically, a context switch involves saving and reloading the following data: • Program counter • Processor status register • Other register contents • User and kernel stack pointers • Pointer to the thread’s address space in which it runs

15. Memory Management • Memory manager provides a variety of services to the OS including: • Virtual memory management • Shared memory and mapped files • Locking memory • Protecting memory

16. Memory Management Continued • Virtual Memory Management • Each user process has a separate 32-bit address space, allowing 4 gigabytes of memory per process. • Yet, 2 gigabytes of this address space is reserved for the OS so the available virtual address space is actually 2 gigabytes.

17. Memory Management Continued • Virtual Memory Management Continued • Pages in a process address are free, reserved, or committed. • Free- not currently being used • Reserved- thread reserves a range of virtual addresses that may be needed in the future • Committed- eventually become valid pages in physical memory, once accessed

18. Memory Management Continued • Shared Memory and Mapped Files • Each process maintains its private memory area, yet the program instructions and unmodified data can be shared without harm. • Implementing shared memory involves the use of shared objects. • Shared objects- represent a block of memory that 2 or more processes can share and can be mapped to the paging file or to another file on disk

19. Memory Management Continued • Locking Memory • Two ways that pages can be locked in memory: • Once pages are locked, they remain in memory until unlocked • Can be locked through the function, VirtualLock • VirtualLock can be called by an application to lock pages in their process working set.

20. Memory Management Continued • Protecting Memory • Prevents user processes from accessing the address space of another process or the OS itself. • Any structures, etc. used by kernel-mode system components are accessible only in kernel mode (not user mode). • Each process has a private address space

21. Memory Management Continued • All processes are supported by some form of hardware-controlled memory protection. • Shared memory section objects have standard access-control lists (ACLs) that are checked when processes attempt to open them. This limits shared memory access to only processes with proper rights.

22. Memory Management Continued • Page Directories • Each process has a single page directory that the memory manager creates to map the location of all page tables for that process. • The physical address of the process page directory is stored in the kernel process block and is also mapped virtually. • Executable code running in kernel mode uses references to virtual, not physical, addresses.

23. Memory Management Continued • Page Directories Continued • The OS constructs a page table, containing the mapping information needed to find the desired page. • In Windows 2000, each process has its own set of process page tables to map that private address space. This is because Win2K provides a private address space for each process.

24. File Management • Main objectives a file management system: • Meets the data management needs and requirements of the user. • Guarantees valid data in the files. • Optimizes performance from the viewpoint of the system and the user. • Provides I/O support for many storage device types. • Helps to eliminates losing or destroying data. • Provides a uniform set of I/O interface routines. • Provides necessary I/O support in times of multiple-user systems.

25. File Management Continued • The only way that a user or application is able to access a file is through the file management system. • Win2K includes support for these file system formats: • CDFS, UDF, FAT12, FAT16, FAT32, NTFS

26. File Management Continued • NTFS • Meets high-end requirements for workstations and servers. • Client/server applications, resource intensive engineering, network applications • Uses 64-bit cluster indexes, yet Win2K limits the size of an NTFS volume to 32-bit clusters.

27. File Management Continued • Notable features of NTFS: • Recoverability, file and directory security, disk quotas, file compression, directory-based symbolic links, and encryption • Many of these support the main objectives for a file management system. • Organizes information into 4 regions on a disk volume: • Partition boot sector, Master file table, System files, File area

28. Threads • Supports user-level and kernel-level threads • Kernel-level threads • User mode kernel-level threads • Created and runs in user mode • Can be preempted by the scheduler • System worker threads • Created by threads and only exist to do work for other threads • Specific types are: delayed worker threads, critical worker threads, and hypercritical worker threads

29. Threads • Kernel-level threads continued • Kernel mode system threads • Have all the attributes of a user mode thread, but can only be run in kernel mode. • Objects running in kernel mode can only create this type of thread. • Has no process address space and must allocate all its storage needs dynamically from the heap- this is different than a user mode system thread.

30. Threads • User-level threads • Created as a normal thread, and then converted to a fiber. • The scheduler does not preemptively schedule different fibers (threads). Instead, a fiber must be switched to from another fiber. • The system can preempt the thread controlling the fiber suspending the execution of the fiber.

31. Mutual Exclusion and Synchronization • Works differently inside and outside of the kernel of Windows 2000. • Within the kernel, much of the mutual exclusion is done using spinlocks. • Outside the kernel, the objects providing mutual exclusion and synchronization rely on services provided by the kernel.

32. Kernel Synchronization • Synchronization in the kernel of Windows 2000 guarantees that only one processor can be executing in a critical section. • Enforced by disabling certain interrupts. • Spinlocks used to protect the core data structures of the kernel.

33. Kernel Synchronization Continued • Mutual exclusion and synchronization within the kernel • Dealt with by modifying how interrupts are handled. • Uses spinlocks • Spinlock- Provides a global data structure in the kernel. Before entering a critical section, the kernel must acquire the spinlock associated with the critical section

34. Kernel Synchronization Continued • Mutual exclusion and synchronization outside the kernel • Executive objects use dispatcher objects (ex- mutexes, semaphores, events, waitable timers) • A thread will issue a wait on one of these objects if it wants to use it. • While waiting, the thread is placed into a suspended state until the dispatcher object enters a signaled state.

35. Summary • Preemptive, multitasking, multiprocessing, multiuser • Scheduling / data management slightly different • Object-driven architecture • Hybrid kernel • Multiple-architecture realized through HAL