Overview of the Windows I/O Model
Every operating system has an implicit or explicit I/O model for handling the flow of data to and from peripheral devices. One feature of the Microsoft Windows I/O model is its support for asynchronous I/O. In addition, the I/O model has the following general features:
The I/O manager presents a consistent interface to all kernel-mode drivers, including lowest-level, intermediate, and file system drivers. All I/O requests to drivers are sent as I/O request packets (IRPs).
I/O operations are layered. The I/O manager exports I/O system services, which user-mode protected subsystems call to carry out I/O operations on behalf of their applications and/or end users. The I/O manager intercepts these calls, sets up one or more IRPs, and routes them through possibly layered drivers to physical devices.
The I/O manager defines a set of standard routines, some required and others optional, that drivers can support. All drivers follow a relatively consistent implementation model, given the differences among peripheral devices and the differing functionality required of bus, function, filter, and file system drivers.
Like the operating system itself, drivers are object-based. Drivers, their devices, and system hardware are represented as objects. The I/O manager and other operating system components export kernel-mode support routines that drivers can call to get work done by manipulating the appropriate objects.
In addition to using IRPs to convey traditional I/O requests, the I/O manager works with the PnP and power managers to send IRPs containing PnP and power requests.
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