yêu cầu hệ thống bao gồm một đơn vị quản lý bộ nhớ (MMU) cho dịch hợp lý để địa chỉ vật lý. Tuy nhiên, MMUs thường làm tăng chi phí và tiêu thụ điện của hệ thống. Ngoài ra, thời gian cần thiết để dịch các địa chỉ hợp lý để vật lý địa chỉ, đặc biệt là trong trường hợp của một bản dịch đệm nhìn sang một bên | System Components 793 kernel-level thread or by an 1SR returning from interrupt processing. Windows XP takes advantage of this property and uses software interrupts to deliver APCs and DPCs to perform system functions such as synchronizing threads with VO completion to start thread dispatches and to handle timers. Executive The Windows XP executive provides a set of services that all environmental subsystems use. The services are grouped as follows object manager virtual memory manager process manager local procedure call facility b Ci manager cache manager security reference monitor plug-and-play and security managers registry and booting. Object Manager For managing kernel-mode entities Windows XP uses a generic set of interfaces that are manipulated by user-mode programs. Windows XP calls these entities objects and the executive component that manipulates them is the object manager. Each process has an object table containing entries that track the objects used by the process. User-mode code accesses these objects using an opaque value called a handle that is returned by many APIs. Object handles can also be created by duplicating an existing handle either from the same process or a different process. Examples of objects are semaphores mutexes events processes and threads. These are all dispatcher objects. Threads can block in the kernel dispatcher waiting for any of these objects to be signaled. The process thread and virtual memory APIs use process and thread handles to identify the process or thread to be operated on. Other examples of objects include files sections ports and various internal I O objects. File objects are vised to maintain the open state of files and devices. Sections are used to map files. Open files are described in terms of file objects. Local-communication endpoints are implemented as port objects. The object manager maintains the Windows XP internal name space. In contrast to UNIX which roots the system name space in
