Plug and Play Overview

Plug and Play in Windows XP Professional allows a user to simply connect a hardware device and leave the job of configuring and starting the hardware to the operating system. However, computer hardware, device drivers, and the system BIOS must all be designed properly in order to install new devices without user intervention. For example, although Windows XP Professional provides Plug and Play functionality, if no Plug and Play capable driver is available for a given device, the operating system cannot automatically configure and start the device.

Note 

In 64-bit computers, BIOS is known as Extensible Firmware Interface (EFI).

When a hardware device is connected, as when a user plugs a USB camera into a USB port, Plug and Play Manager goes through the following steps to successfully install the device:

• After receiving an insertion notification, Plug and Play Manager checks what hardware resources the device needs (such as interrupts, memory ranges, I/O ranges, and DMA channels) and to assign those resources.

• Plug and Play Manager checks the hardware identification number of the device. It then checks the hard drive, floppy drives, CD ROM drive, and Windows Update for a driver that matches the hardware identification number of the device.

• If multiple drivers are found, Plug and Play Manager chooses the optimal driver by looking for the closest hardware ID or compatible ID match, driver signatures, and other driver features, and then installs the driver and starts the device.

Device drivers included with or installed under Windows XP Professional must meet the standards of the Windows Logo program. Device drivers that have passed the Windows Hardware Quality Lab (WHQL) compatibility tests are electronically signed and Windows XP Professional detects the digital signature. For system stability, it is recommended that you use only signed device drivers with Windows XP Professional. A message notifies the user if an unsigned driver is being installed.

When multiple drivers are available for a given device, Windows XP Professional uses driver-ranking schemes to determine the optimal driver to load. Driver rank is established based on whether the driver is signed and how closely the driver s Plug and Play ID matches the device s Plug and Play ID.

For more information about Driver Signing, see Windows Update and Driver Signing later in this chapter. For more information about driver-ranking schemes, see Driver Ranking later in this chapter.

The extent of Plug and Play support depends on both the hardware device and the device driver. For example, an older device that is not Plug and Play such as a manually configured Industry Standard Architecture (ISA) sound card or an Extended Industry Standard Architecture (EISA) network adapter can gain functionality from a Plug and Play driver.

If a driver does not support Plug and Play, its devices behave as non Plug and Play devices. This might result in the loss of some operating system functionality. For example, power management features such as hibernation might not work.

Note 

For monitors, Windows XP Professional supports Plug and Play installation only when the monitor, the display adapter, and the display driver are Plug and Play; otherwise, the monitor is detected as Default Monitor.

If you connect the monitor by using a switch box, Plug and Play attributes of the monitor might be lost.

In Windows XP Professional, Plug and Play support is optimized for computers that include an Advanced Configuration and Power Interface (ACPI) BIOS. The ACPI BIOS is responsible for tasks such as describing hardware that is not visible to Plug and Play because the hardware is connected to a bus that does not support Plug and Play. For example, the ACPI BIOS describes and helps in configuring devices such as system timers and programmable interrupt controllers on the motherboard, which is not on a bus that supports Plug and Play.

For all Plug and Play features to work on a given system, it must include an ACPI BIOS and hardware devices and drivers that are Plug and Play compliant. An Advanced Power Management (APM) BIOS or a Plug and Play BIOS does not enable all Plug and Play features and is not as robust as ACPI.

When you troubleshoot or manually change resource settings, it is helpful to know whether Plug and Play functionality is provided by the operating system or by the BIOS. If Plug and Play is handled by the BIOS and you manually change resources that are allocated to hardware devices (such as interrupts or memory ranges) these changes become fixed, and the operating system cannot reallocate those resources. When any hardware resource is fixed, Windows XP Professional loses some of its ability to optimally allocate resources among all devices in the system. When Windows XP Professional cannot optimally allocate all resources, the likelihood is increased that one or more devices might not function properly due to resource allocation problems.

For more information about ACPI, see the ACPI link on the Web Resources page at http://www.microsoft.com/windows/reskits/webresources and Power Management later in this chapter.

On x86-based computers, the way that the system BIOS code interacts with Plug and Play devices depends on whether the system BIOS or the operating system configures hardware. If your computer has this option, the setting for the Enable Plug and Play operating system switch can affect this interaction.

For more information about setting Plug and Play BIOS settings, see Setting Plug and Play BIOS Settings later in this chapter.

Note 

A motherboard with Itanium-based architecture relies on ACPI and the operating system to configure resources. The option to enable or disable ACPI functionality is not available on Itanium-based computers.

Some Plug and Play devices can be installed or removed while the system is running. For example, USB, IEEE 1394 and PC Card devices can be added to and removed from a fully powered system. When such hardware is added or removed, the operating system automatically detects insertion or removal of the device and manages system and/or hardware configuration as required. If the device is not designed to be removed while the system is running, it is recommended that you notify the operating system in advance to avoid problems. The Safely Remove Hardware application notifies the operating system that a device will be removed.

Table 9-1 shows the different types of Plug and Play devices, and whether or not they can be removed while the system is turned on.

Table 9-1: Plug and Play Device Connections and Installation Guidelines

Devices on these buses or connectors	Can be added to or removed from a running system	System must be turned off before device is added/ removed from system
USB, IEEE 1394, PC Card devices, CardBus devices	Yes Remove hardware by using the Safely Remove Hardware application if it appears in the notification area.	No
PCI, ISA, EISA	No	Yes
Docking station	Varies among computer manufacturers; most support docking and undocking while the computer is running.	Varies among computer manufacturers; most support docking and undocking while the computer is running.

For more information about the Safely Remove Hardware application, see Safe Removal of Plug and Play Devices later in this chapter. For information about the Hot Undocking feature for portable computers, see Supporting Mobile Users in this book.