Troubleshooting Hardware Conflicts

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Windows 95 Professional

A publication of The Cobb Group

Published March 1998

If your organization is on a tight budget and your users need more computing power, you may be forced to upgrade the existing systems rather than buying new ones. The once simple task of upgrading systems is now more complex than ever because of the variety of hardware devices available. Many times, the process will result in a seemingly unresolvable hardware conflict.

In this article, we'll provide you with some tips and techniques you can use to troubleshoot these types of conflicts in Windows 95. We'll begin by looking at the different types of devices available and what components usually cause conflicts.

On This Page

Hardware background
What causes conflicts?
Compiling a list
Tracking down the problem
Resolving simple conflicts
Resolving complex conflicts

Hardware background

As you probably know, you can upgrade many different components in your computer. For example, you can install a larger hard disk, more memory, or a faster processor. However, these types of components rarely cause conflicts in your system. The device that's responsible for the most conflicts is the expansion card. There are three basic types of expansion cards— jumpered, software configurable, and Plug and Play.

Jumpered cards

Jumpered cards are the oldest type of expansion cards. To configure these cards, you must move a small device called a jumper to a specific set of pins on the card. This jumper makes an electrical connection between the two pins.

Software configurable cards

Software configurable cards have no jumpers that you can manually set. Instead, you must install the card, boot your system (usually in DOS mode), and run a special utility to configure the card.

Plug and Play cards

Plug and Play is the newest type of expansion card. The idea behind Plug and Play is that Windows 95 can automatically recognize and configure the card for optimum performance.

What causes conflicts?

A hardware conflict is usually caused by two cards interfering with each other. Typically, the two cards are both trying to use the same resource, such as a hardware interrupt request line (IRQ) or a memory address. Let's take a closer look.

IRQ conflicts

An IRQ provides hardware devices inside the system with a direct line to the microprocessor. Basically, hardware devices use an IRQ to signal the microprocessor, request that it stop what it's doing, and ask it to perform a task. For example, if the microprocessor is processing data from a spreadsheet and an E-mail message arrives, the network card will request that the microprocessor stop and immediately route the message to your E-mail application.

X86 and Pentium systems have 16 IRQs, which are prioritized according to the importance of the device. As you can see in Table A, many of the IRQs are dedicated to specific devices and thus unavailable. Problems arise because each interrupt can be used for only one device.

Table A The 16 IRQs in X86 and Pentium systems


Type of bus slot

Standard function



System timer



Keyboard controller



Second IRQ controller



COM port 2 (or COM 4, if installed/enabled)



COM port 1 (or COM 3, if installed/enabled)



Parallel port (LPT 2, if installed/enabled)



Floppy disk controller



Parallel port (LPT 1)



Real-time clock



Available (redirected IRQ 2)









PS/2 mouse port (if installed/enabled)



Math coprocessor



Hard disk controller




For example, if you assign IRQ 5 to a sound card, you won't be able to assign that IRQ to a network card. Occasionally you may find that two devices can share an IRQ if you don't use the devices simultaneously. However, this setup usually isn't a good idea and should be done only when all 16 IRQ's are filled.

Memory address conflicts

The other resource that two cards can fight over is a memory address (usually a range of memory addresses). The same rules apply to memory addresses that apply to IRQs. Basically, two cards can't use the same memory address. To resolve this type of conflict, simply reconfigure the cards to use unique addresses.

Compiling a list

Now that you have a good understanding of what causes conflicts, let's take a look at how you go can prevent them from occurring. To begin, you'll want to compile a list of all the IRQs and memory addresses in use by your system. Then, you'll be able to use this information to determine what IRQs and memory addresses are available. Fortunately, you can find this information in Device Manager.

To access Device Manager, launch Control Panel and double-click the System icon. (You can also open this utility by right-clicking My Computer and selecting Properties from the shortcut menu.) When the System Properties sheet appears, select the Device Manager tab. You'll then see a tree list of all the devices in your system, as shown in Figure A.


Figure A: Device Manager lists all the devices installed on your system.

At the very top of Device Manager's list of devices, you'll notice an icon titled simply Computer. If you double-click this icon, you'll discover a detailed listing of your system's resources including IRQ settings, as shown in Figure B, and memory addresses.


Figure B: The View Resources tab provides a detailed listing of your system's resources.

If you have jumpered cards in your system, you should make sure the card's settings match what Device Manager indicates. To do so, you'll have to shut down the system, remove the cards, and physically examine each one.

Likewise, if you have software configurable cards, we recommend that you run the configuration program that came with each card and record the card's settings. You should run this program in DOS mode if possible (but not from a command prompt window). Then, make sure that the two sets of numbers match.

Tracking down the problem

Once you've compiled a list of IRQs and memory addresses, you can return to Device Manager. If Device Manager discovers a conflict, it will pinpoint the malfunctioning device with a yellow circle and an exclamation point, as shown in Figure C. You can then find detailed information about the conflict by selecting the malfunctioning device and clicking the Properties button. Many times, the device's properties sheet will contain a Resources tab, such as the one shown in Figure D, which lists the resources that Windows 95 thinks the card is using. We'll explain this in more detail in a moment when we discuss misidentified resources.


Figure C: A yellow circle with an exclamation point indicates a malfunctioning device.


Figure D: The Resources tab displays the settings that Windows 95 thinks the card is using.

Resolving simple conflicts

Sometimes the conflicts that prevent a device from working properly are easy to resolve. Let's examine a few of the most common conflicts and their fixes.

Misidentified resources

If Device Manager indicates that a card is using different resources than those you've manually configured, you need to reconfigure Windows 95's settings to match the settings you've manually configured. To do so, select the device in the Device manager tab and click the Properties button. When you see the device's properties sheet, select the Resources tab. Then, deselect the Use Automatic Settings check box. Next, select the appropriate resource and click the Change Setting… button. You can now change Windows 95's settings to match the card's settings.

The Conflicting Device List box at the bottom of the dialog box displays any known conflicts between the new settings and any other devices in your system. Although this section is handy, it's not always reliable because it receives the conflict information from Windows 95's configuration settings rather than the card's actual configuration settings.

For example, suppose you discover that you have two cards whose Windows 95 settings don't match the cards' actual settings. When you change the first card to match its physical configuration, Windows 95 may erroneously report a conflict because of the incorrect configuration information for the second card. When you try to save your changes, Windows 95 may balk. To resolve the problem, try changing the second card's settings and then come back to the first one.

IRQ contention

If you determine that two cards are sharing the same IRQ, you should reconfigure one of the cards to use an available IRQ. Keep in mind that not all cards can use just any available IRQ.

For example, suppose you have a sound card and a network card that are both set to use IRQ 5. You might look at your list of available IRQs and see that IRQ 7 is available. Normally, you'd simply reconfigure one of the cards to use IRQ 7 instead of IRQ 5. Unfortunately, you may run into cases in which neither card can be configured to use this IRQ. If that happens, you'll have to try other IRQs.

Resolving complex conflicts

At this point, we're assuming that you have no known IRQ or memory conflicts, that your Windows 95 configuration information matches your physical configuration, and that you're still having some sort of hardware problem. If this is the case, the problem is usually an incorrectly configured Plug and Play device.

To determine if this is the case, remove any Plug and Play cards from your system and reboot to Windows 95. More than likely, the problem will go away. If so, shut down your system again, reinstall one of the Plug and Play devices, boot the system into Windows 95, and test for the error. If the conflict returns, you can use Device Manager to override the Plug and Play settings and manually reconfigure the card. The big difference in this situation is that although the configuration information you provide must still be unique, it doesn't have to match the card's physical configuration. Instead, Windows 95 will automatically reconfigure the card to use the settings you've assigned. Now, shut down Windows 95 and install and test each remaining card—one at a time.

It's very important to make sure that everything else is working correctly before you attempt to reconfigure Plug-and-Play devices. Otherwise, Windows 95 may automatically undo all the configuration settings you've worked so hard to figure out. Second, you should always install Plug-and-Play cards one at a time. If you don't, Windows 95 may get confused.


In this article, we've shown you how to troubleshoot hardware conflicts in Windows 95. You should be able to resolve most conflicts by following the guidelines we've provided.

The article entitled "Troubleshooting hardware conflicts" was originally published in Windows 95 Professional, March 1998. Copyright © 1988, The Cobb Group, 9420 Bunson Parkway, Louisville, KY 40220. All rights reserved. For subscription information, call the Cobb Group at 1-800-223-8720.

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