Windows® Internals, Sixth Edition, Part 2

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Last but not least, thanks to Ben Ryan, publisher of Microsoft Press, who continues to believe in the importance of continuing to provide this level of detail about Windows to their readers!

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Chapter 8. I/O System

The Windows I/O system consists of several executive components that together manage hardware devices and provide interfaces to hardware devices for applications and the system. In this chapter, we’ll first list the design goals of the I/O system, which have influenced its implementation. We’ll then cover the components that make up the I/O system, including the I/O manager, Plug and Play (PnP) manager, and power manager. Then we’ll examine the structure and components of the I/O system and the various types of device drivers. We’ll look at the key data structures that describe devices, device drivers, and I/O requests, after which we’ll describe the steps necessary to complete I/O requests as they move through the system. Finally, we’ll present the way device detection, driver installation, and power management work.

I/O System Components

The design goals for the Windows I/O system are to provide an abstraction of devices, both hardware (physical) and software (virtual or logical), to applications with the following features:

Uniform security and naming across devices to protect shareable resources. (See Chapter 6, “Security,” in Part 1 for a description of the Windows security model.)

High-performance asynchronous packet-based I/O to allow for the implementation of scalable applications.

Services that allow drivers to be written in a high-level language and easily ported between different machine architectures.

Layering and extensibility to allow for the addition of drivers that transparently modify the behavior of other drivers or devices, without requiring any changes to the driver whose behavior or device is modified.

Dynamic loading and unloading of device drivers so that drivers can be loaded on demand and not consume system resources when unneeded.

Support for Plug and Play, where the system locates and installs drivers for newly detected hardware, assigns them hardware resources they require, and also allows applications to discover and activate device interfaces.

Support for power management so that the system or individual devices can enter low power states.

Support for multiple installable file systems, including FAT, the CD-ROM file system (CDFS), the Universal Disk Format (UDF) file system, and the Windows file system (NTFS). (See Chapter 12, for more specific information on file system types and architecture.)

Windows Management Instrumentation (WMI) support and diagnosability so that drivers can be managed and monitored through WMI applications and scripts. (WMI is described in Chapter 4, “Management Mechanisms,” in Part 1.)

To implement these features the Windows I/O system consists of several executive components as well as device drivers, which are shown in Figure 8-1.

The I/O manager is the heart of the I/O system. It connects applications and system components to virtual, logical, and physical devices, and it defines the infrastructure that supports device drivers.