System Components — Kernel

Kernel — Process and Threads

The process has a virtual memory address space, information (such as a base priority), and an affinity for one or more processors.

Threads are the unit of execution scheduled by the kernel’s dispatcher.

Each thread has its own state, including a priority, processor affinity, and accounting information.

A thread can be one of six states: ready, standby, running, waiting, transition, and terminated.

Kernel — Scheduling

The dispatcher uses a 32-level priority scheme to determine the order of thread execution. Priorities are divided into two classes..

    1. The real-time class contains threads with priorities ranging from 16 to 32.

    2. The variable class contains threads having priorities from 0 to 15.

Characteristics of 2000’s priority strategy.

    1. Trends to give very good response times to interactive threads that are using the mouse

         and windows.

    2. Enables I/O-bound threads to keep the I/O devices busy.

    3.Complete-bound threads soak up the spare CPU cycles in the background.

Scheduling can occur when a thread enters the ready or wait state, when a thread terminates, or when an application changes a thread’s priority or processor affinity.

Real-time threads are given preferential access to the CPU; but 2000 does not guarantee that a real-time thread will start to execute within any particular time limit.

Kernel — Trap Handling

The kernel provides trap handling when exceptions and interrupts are generated by hardware of software.

Exceptions that cannot be handled by the trap handler are handled by the kernel's exception dispatcher.

The interrupt dispatcher in the kernel handles interrupts by calling either an interrupt service routine (such as in a device driver) or an internal kernel routine.

The kernel uses spin locks that reside in global memory to achieve multiprocessor mutual exclusion.

Executive — Object Manager

2000 uses objects for all its services and entities; the object manger supervises the use of all the objects.

       1. Generates an object handle

       2. Checks security.

       3. Keeps track of which processes are using each object.

Objects are manipulated by a standard set of methods, namely create, open, close, delete, query name, parse and security.

Executive — Naming Objects

The 2000 executive allows any object to be given a name, which may be either permanent or temporary.

Object names are structured like file path names in MS-DOS and UNIX.

2000 implements a symbolic link object, which is similar to symbolic links in UNIX that allow multiple nicknames or aliases to refer to the same file.

A process gets an object handle by creating an object by opening an existing one, by receiving a duplicated handle from another process, or by inheriting a handle from a parent process.

Each object is protected by an access control list.

Executive — Virtual Memory Manager

The design of the VM manager assumes that the underlying hardware supports virtual to physical mapping

a paging mechanism, transparent cache coherence on multiprocessor systems, and virtual addressing aliasing.

The VM manager in 2000 uses a page-based management scheme with a page size of 4 KB.

The 2000 VM manager uses a two step process to allocate memory.

      1. The first step reserves a portion of the process’s address space.

      2. The second step commits the allocation by assigning space in the 2000 paging file.

Virtual-Memory Layout

The virtual address translation in 2000 uses several data structures.

      1. Each process has a page directory that contains 1024 page directory entries of size 4

          bytes.

      2. Each page directory entry points to a page table which contains 1024 page table entries

           (PTEs) of size 4 bytes.

      3. Each PTE points to a 4 KB page frame in physical memory.

A 10-bit integer can represent all the values form 0 to 1023, therefore, can select any entry in the page directory, or in a page table.

This property is used when translating a virtual address pointer to a bye address in physical memory.

A page can be in one of six states: valid, zeroed, free standby, modified and bad.

Virtual-to-Physical Address Translation

10 bits for page directory entry, 20 bits for page table entry, and 12 bits for byte offset in page.

 Page File Page-Table Entry

5 bits for page protection, 20 bits for page frame address, 4 bits to select a paging file, and 3 bits that describe the page state. V = 0

Executive — Process Manager

Provides services for creating, deleting, and using threads and processes.

Issues such as parent/child relationships or process hierarchies are left to the particular environmental subsystem that owns the process.

Executive — Local Procedure Call Facility

The LPC passes requests and results between client and server processes within a single machine.

In particular, it is used to request services from the various 2000 subsystems.

When a LPC channel is created, one of three types of message passing techniques must be specified.

        1. First type is suitable for small messages, up to 256 bytes; port's message queue is used 

             intermediate storage, and the messages are copied  from one process to the other.

        2. Second type avoids copying large messages by pointing to a shared memory section

            object created for the channel.

        3. Third method, called quick LPC was used by graphical display portions of the Win32

              subsystem.

Executive — I/O Manager

The I/O manager is responsible for

        1. file systems

        2. cache management

        3. device drivers

        4. network drivers

Keeps track of which installable file systems are loaded, and manages buffers for I/O requests.

Works with VM Manager to provide memory-mapped file I/O.

Controls the 2000 cache manager, which handles caching for the entire I/O system.

Supports both synchronous and asynchronous operations, provides time outs for drivers, and has mechanisms for one driver to call another.

File I/O

Executive — Security Reference Manager

The object-oriented nature of 2000 enables the use of a uniform mechanism to perform 

runtime access validation and audit checks for every entity in the system.

Whenever a process opens a handle to an object, the security reference monitor checks the process’s security token and the object’s access control list to see whether the process has the necessary rights.