PC Hacks 100 Industrial-Strength Tips and Tools

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Hack 18 Reeducate Plug and Play

The Microsoft Windows Plug and Play BIOS extension generally knows when a new device is installed, as you can see in Microsoft Windows when a "New hardware found" dialog appears, but it doesn't know if you've changed the configuration of a device through its configuration/setup program or using Windows Device Manager.

It is possible, depending on the capabilities of the respective device drivers (usually for PCI network and SCSI cards), to reconfigure an I/O device through Device Manager. This reconfiguration is not dynamic: Windows won't really know about it until Plug and Play BIOS tells it things have changed. That only happens at bootup, and sometimes only if the BIOS is told to look for the change. Merely changing a device's internal configuration does not constitute a new or removed device in Plug and Play's "mind," and it never gets it without some help.

To tell Plug and Play that things have changed by adding or removing an I/O device, or by "soft" changes you made within Windows, you have to reboot your system, enter the BIOS setup, and then force Plug and Play to reassess the system configuration. This gets the BIOS to reconfigure the system properly, and informs the operating system of the changes.

Reeducating Plug and Play is done by a parameter most often named "Reset Configuration Data" or "Reset NVRAM" (non-volatile RAM). NVRAM is an area of memory on the system board that stores Plug and Play data. Make sure that Plug and Play OS is set to Yes (provided you have a Plug and Play-compliant operating system, such as Windows), set the Reset value to Yes, and then restart your PC. The BIOS will reevaluate the system configuration, store any new data, and make it available to the operating system (see Figure 2-9).

Figure 2-9. Resetting the configuration data forces Plug and Play to roll the dice again to reset device configurations based on new settings

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