HP 752c (US/CAN) manual Windows 2000 White Paper

request to be turned off, the Power Manager collects those requests, determines

which requests must be serialized, and then generates appropriate power :'0management￿,QWHUIDFHIRPs. ￿IRU￿3OXJ￿DQG￿3OD\

The Policy Manager monitors activity in the system and integrates user status, application status, and device driver status into power policy. Under specified circumstances or upon request, the Policy Manager generates IRPs to change ,device￿2￿0DQDJHUpower states.

The I/O Manager provides core services for device drivers. The I/O Manager is the kernel-mode component that translates user-mode read and write commands into read or write IRPs. It manages all the other main operating system IRPs. These interfaces work as they did in Windows NT 4.0. Because both Windows NT 4.0 and Windows 2000 include the I/O manager, a Plug and Play driver can be manually installed on Windows NT 4. and can function as a Windows 2000 Plug and Play driver.

The I/O system provides a layered architecture for drivers. This section discusses types of WDM drivers, driver layers, and device objects. For a different discussion of the topics covered in this section, see the Introduction to Plug and Play Help file 7\SHVin the Windows￿RI￿'ULYHUV98 DDK Preview.

From the Plug and Play perspective, there are three kinds of drivers:

∙A bus driver services a bus controller, adapter, bridge, or any device that has child devices. Bus drivers are required drivers and are generally provided by Microsoft; there is one bus driver for each type of bus on a system.

∙A function driver is the main device driver and provides the operational interface for its device. It is a required driver unless the device is used raw (an implementation in which I/O is done by the bus driver and any bus filter drivers). The function driver for a device is typically implemented as a driver/minidriver pair. In such driver pairs, a class driver (usually written by Microsoft) provides the functionality required by all devices of that type, and a minidriver (usually written by the device vendor) provides device-specific functionality. The Plug and Play Manager loads one function driver for each device.

∙A filter driver sorts I/O requests for a bus, a device, or a class of devices. Filter drivers are optional and can exist in any number, placed above or below a function driver and above a bus driver. Usually, filter drivers are supplied by system OEMs or independent hardware vendors (IHVs).

In most cases, lower-level filter drivers modify the behavior of device hardware. For example, a lower-level class filter driver for mouse devices could provide acceleration, performing a non-linear conversion of mouse movement data.