Tài liệu Registry and Plug and Play Subsystem pptx

Registry and Plug and Play Subsystem

At the end of Chapter 1, there was a simple example providing a general understanding of

the process used by the system to install new devices and resolve hardware conflicts.

However, this example was overly simplistic and, more importantly, covered the process

of hardware installation only from the user's point of view. But what actually happens

when the system installs new hardware? What components are required to accomplish

this task? How should we configure hardware and resolve hardware conflicts? These are

clearly topics of great interest to anyone who is initiating full-scale support for Windows

XP and Windows Server 2003. With the release of Windows 95, Microsoft introduced a

new concept for simplifying PC usage: Plug and Play (or PnP). What is Plug and Play? A

standard, a specification, or a concept? Actually, Plug and Play is a combination of the

general approach to designing PCs and a set of specifications describing the hardware

architecture. Strictly speaking, it is a combination of the system BIOS, hardware devices,

system resources, device drivers, and the operating-system software.

All Plug and Play components have the same purpose: to facilitate the automatic

functioning of the PC, peripheral devices, and their drivers, with a minimum of

intervention from the user. Users working with systems that meet all Plug and Play

requirements don't have to spend time wondering if a newly installed device will create

hardware conflicts with another device. The registry provides the basis for developing

such a system.

The HKEY_LOCAL_MACHINE/HARDWARE registry key contains a description of

the system hardware and the relationship between hardware devices and their drivers.

Before we go any further, you should note that this key is volatile and that all of the

information it contains is re-created every time the operating system is booted.

The hardware recognizer (Ntdetect.com) collects information related to system hardware,

and the OS kernel stores the information under the

HKEY_LOCAL_MACHINE\HARDWARE\DESCRIPTION registry key. As the drivers

are loading, they pass their information on to the system so that it can associate the

hardware devices and their appropriate drivers. The operating system saves this

information under the HKLM\HARDWARE\DEVICEMAP registry key. Finally, all the

necessary information related to resources for the hardware devices (including ports,

DMA addresses, IRQs) is stored under HKLM\HARDWARE\RESOURCEMAP.

With the arrival of Windows 2000, two new Executive subsystems were introduced: Plug

and Play Manager and Power Manager. Plug and Play Manager is integrated with the I/O

Manager and doesn't participate in the initialization process. However, the drivers are

initialized in such a way that Plug and Play drivers recognize some hardware devices.

Windows NT 4.0, on the other hand, uses only Ntdetect.com to recognize hardware

devices, because of its limited Plug and Play support.

Though Windows XP and Windows Server 2003 are based on the Windows NT/2000

kernel, the Plug and Play support provided by these newer operating systems has been

further enhanced, improved, and optimized. The general idea of this design was to

combine the respective advantages of the two lines of Windows products — Windows

NT/2000 and Windows Millennium Edition (Windows ME). The approach has been a

success, providing greater stability in the OS and delivering better device compatibility.

For the moment, Windows XP and Windows Server 2003 include Plug and Play support

for hundreds of devices not recognized by Windows 2000, including scanners, cameras,

audio devices, storage devices, and media (CDs and DVDs). At the same time, these

systems also provide better support for Universal Serial Bus (USB), IEEE 1394,

Peripheral Component Interconnects (PCI), and other buses. Improvements introduced in

the Plug and Play subsystem have lead to better stability and performance. This is

especially true with regard to the device-installation process, which has been streamlined

and automated, as shown in the example in Chapter 1. Beside this, power-management

support has also been improved, which is of benefit to both desktop and mobile computer

users.

Plug and Play Historical Overview

Plug and Play is a technology that allows the automatic configuration of the PC and all of

the devices installed on the system. It allows you to start using newly installed hardware

(for example, a sound card or modem) immediately after installation, and without having

to configure the device manually. Plug and Play operates at the hardware level, the

operating-system level and in the device drivers and BIOS.

The introduction of Plug and Play was the result of cooperation between software and

hardware vendors, who created an industrial committee in order to unite their efforts.

This committee was founded in May of 1993, and initially included three corporations:

Microsoft, Intel, and Compaq. By the end of 1995, a number of vendors were already

producing hundreds of hardware devices complying with this standard.

Microsoft® Windows® 95 was the first operating system that implemented Plug and

Play support. However, since then, PnP standards have undergone a significant evolution,

mainly as a result of the efforts of the members of the OnNow industry initiative. OnNow

is aimed at identifying a standardized approach to controlling both the operating system

and hardware-device configuration. The main achievement of OnNow has been the

Advanced Configuration and Power Interface (ACPI) Version 1.0 specification, which

defines the basic interface between the motherboard and the system BIOS. This interface