Adapter boards use upper memory for their BIOS and as working RAM. If two boards attempt to use the same BIOS area or RAM area of upper memory, a conflict occurs that can keep your system from booting. In most cases, the plug-and-play software in the operating system ensures that such cards are automatically reconfigured so that they are not in conflict; however, sometimes problems can occur and you must step in and manually resolve a conflict. The following sections cover ways to avoid these potential unresolved conflicts and how to troubleshoot if they do occur. In addition, these sections discuss moving adapter memory to resolve conflicts and provide some ideas on optimizing adapter memory use.

How to Determine What Adapters Occupy the UMA

You can determine which adapters are using space in upper memory in the following two ways:

• Study the documentation for each adapter on your system to determine the memory addresses they use.

• Use a software utility or the Device Manager in your operating system to determine which upper memory areas your adapters are using.

The simplest way (although by no means always the most foolproof) is to use a software utility to determine the upper memory areas used by the adapters installed on your system. The Device Manager in the Windows 9x/Me and 2000/XP Control Panel supplies this information in great detail, as does the System Information utility (MSInfo32) that comes with Windows 98 and later. These utilities examine your system configuration and determine not only the upper memory used by your adapters, but also the IRQs used by each of these adapters.

True plug-and-play systems also shut down one of the cards involved in a conflict to prevent a total system lockup. This could cause Windows to boot in safe mode.

After you run Device Manager, System Information, or another utility to determine your system's upper memory configuration, make a printout of the memory addresses used. Thereafter, you can quickly refer to the printout when you are adding a new adapter to ensure that the new board does not conflict with any devices already installed on your system.

Moving Adapter Memory to Resolve Conflicts

After you identify a conflict or potential conflict using one of the two methods discussed in the previous section, you might have to reconfigure one or more of your adapters to move the upper memory space used by a problem adapter.

Most non-PnP adapter boards make moving adapter memory a somewhat simple process, enabling you to change a few jumpers or switches to reconfigure the board. With plug-and-play cards, use the configuration program that comes with the board or the Windows Device Manager to make the changes. The following steps help you resolve most problems that arise because adapter boards conflict with one another:

For example, if one adapter uses the upper memory range C8000CBFFF and another adapter uses the range CA000CCFFF, you have a potential address conflict. One of them must be changed. Note that plug-and-play cards allow these changes to be made directly from the Windows Device Manager.