The incredible acceptance and popularity of the PC is largely due to the use of an "open architecture". An open architecture allows any manufacturer to develop new devices (i.e. video boards, modems, sound boards, and so on) that will work in conjunction with the PC. When a new expansion board is added to the PC, the board makes use of various system resources in order to obtain CPU time and transfer data across the expansion bus. Ultimately, each board that is added to the system requires unique resources. No two devices can use the same resources - otherwise, a hardware conflict will result. Low-level software (such as device drivers and TSRs) that uses system resources can also conflict with one another during normal operation. This chapter explains system resources, then shows you how to detect and correct conflicts that can arise in both hardware and software.

The key to understanding and eliminating conflicts is to understand the importance of each system resource that is available to you. PCs provide three types of resources; interrupts, DMA channels, and I/O areas. Many controllers and network devices also utilize BIOS which requires memory space. Do not underestimate the importance of these areas - conflicts can occur anywhere, and carry dire consequences for a system.

An interrupt is probably the most well-known and understood type of resource. Interrupts are used to demand attention from the CPU. This allows a device or sub-system to work in the background until a particular event occurs which requires system processing. Such an event my include receiving a character at the serial port, striking a key on the keyboard, or any number of other real-world situations. An interrupt is invoked by asserting a logic level on one of the physical interrupt request (IRQ) lines accessible through any of the motherboard’s expansion bus slots. AT-compatible PCs provide 16 IRQ lines (noted IRQ 0 to IRQ 15). Table 13-1 illustrates the IRQ assignments for classic XT and current AT systems. These lines run from pins on the expansion bus connector or key ICs on the motherboard to Programmable Interrupt Controllers (PICs) on the motherboard. The output signals generated by a PIC triggers the CPU interrupt. Keep in mind that Table 13-1 covers hardware interrupts only. There are also a proliferation of processor and software-generated interrupts.

The use of IRQ 2 in an AT system deserves a bit of explanation. An AT uses IRQ 2 right on the motherboard, which means the expansion bus pin for IRQ 2 is now empty. Instead of leaving this pin unused, IRQ 9 from the AT extended slot is wired to the pin previously occupied by IRQ 2. In other words, IRQ 9 is being redirected to IRQ 2. Any AT expansion device set to use IRQ 2 is actually using IRQ 9. Of course, the vector interrupt table is adjusted to compensate for this slight-of-hand.

After an interrupt is triggered, an interrupt handling routine saves the current CPU register states to a small area of memory (called the stack), then directs the CPU to the interrupt vector table. The interrupt vector table is a list of program locations that correspond to each interrupt. When an interrupt occurs, the CPU will jump to the interrupt handler routine at the location specified in the interrupt vector table and execute the routine. In most cases, the interrupt handler is a device driver associated with the board generating the interrupt. For example, an IRQ from a network card will likely call a network device driver to operate the card. For a hard disk controller, an IRQ calls the BIOS ROM code that operates the drive. When the handling routine is finished, the CPU's original register contents are "popped" from the stack, and the CPU picks up from where it left off without interruption.

As a technician, it is not vital that you understand precisely how interrupts are initialized and enabled, but you should know the basic terminology. The term "assigned"simply means that a device is set to produce a particular IRQ signal. For example, a typical hard drive controller board is assigned to IRQ 14. Assignments are usually made with one or more jumpers or DIP switches, or are configured automatically through the use of Plug-and-Play (PnP). Next, interrupts can be selectively enabled or disabled under software control. An "enabled" interrupt is an interrupt where the PIC has been programmed to pass on an IRQ to the CPU. Just because an interrupt is enabled does not mean that there are any devices assigned to it. Finally, an "active" interrupt is a line where real IRQs are being generated. Note that active does not mean assigned or enabled.

Interrupts are an effective and reliable means of signaling the CPU, but the conventional ISA bus architecture - used in virtually all PCs - does not provide a means of determining which slot contains the board that called the interrupt. As a result, interrupts cannot be shared by multiple devices. In other words, no two devices can be actively generating interrupt requests on the same IRQ line at the same time. If more than one device is assigned to the same interrupt line, a hardware conflict can occur. In most circumstances, a conflict may prevent the newly installed board (or other previously installed boards) from working. In some cases, a hardware conflict can hang up the entire system.

The MCA (micro channel architecture) and EISA (Extended ISA) busses overcome this IRQ sharing limitation, but MCA was never widely accepted in the PC industry because the slots are not backwardly compatible with the well-established base of ISA boards. EISA bus slots are backwardly compatible with ISA boards, but an ISA board in an EISA slot was still faced with the same IRQ limitations.

The CPU is very adept at moving data. It can transfer data between memory locations, I/O locations, or from memory to I/O and back with equal ease. However, PC designers realized that transferring large amounts of data (one word at a time) through the CPU is a hideous waste of CPU time. After all, the CPU really isn't processing anything during a data move, just shuttling data from one place to another. If there were a way to "off-load" such redundant tasks from the CPU, data could be moved faster than would be possible with CPU intervention. Direct Memory Access (DMA) is technique designed to move large amounts of data from memory to an I/O location, or vice versa, without the direct intervention by the CPU. In theory, the DMA controller IC acts as a stand-alone "data processor", leaving the CPU free to handle other tasks.

A DMA transfer starts with a DMA Request (DRQ) signal generated by the requesting device (such as the floppy disk controller board). If the channel has been previously enabled through software drivers or BIOS routines, the request will reach the corresponding DMA controller IC on the motherboard. The DMA controller will then send a HOLD request to the CPU, which responds with a Hold Acknowledge (HLDA) signal. When the DMA controller receives the HLDA signal, it instructs the bus controller to effectively disconnect the CPU from the expansion bus and allow the DMA controller IC to take control of the bus itself. The DMA controller sends a DMA Acknowledge (DACK) signal to the requesting device, and the transfer process may begin. Up to 64KB can be moved during a single DMA transfer. After the transfer is done, the DMA controller will reconnect the CPU and drop its HOLD request - the CPU then continues with whatever it was doing without interruption.

Table 13-2 illustrates the use of DMA channels for both classic XT and current AT systems. There are twice as many DMA channels available in an AT than an XT, but you may wonder why the AT commits fewer channels. The issue is DMA performance. DMA was developed when CPUs ran at 4.77MHz, and is artificially limited to 4MHz operation. When CPUs began to work at 8MHz and higher, CPU transfers (redundant as they are) actually became faster than a DMA channel. As a result, the AT has many channels available, but only the floppy drive controller and other limited-performance devices (such as sound cards) continue to use DMA. In an AT system, DMA channel 4 serves as a cascade line linking DMA controller ICs.

As with interrupts, a DMA channel is selected by setting a physical jumper or DIP switch on the particular expansion board (or through Plug-and-Play). When the board is installed in an expansion slot, the channel setting establishes a connection between the board and DMA controller IC. Often, accompanying software drivers must use a command line switch that points to the correcponding hardware DMA assignment. Also, DMA channels can not be shared between two or more devices. Although DMA sharing is possible in theory, it is extremely difficult to implement in actual practice. If more than one device attempts to use the same DMA channel at the same time, a conflict will result.

Both XT and AT computers provide space for I/O (input/output) ports. An I/O port acts very much like a memory address, but it is not for storage. Instead, an I/O port provides the means for a PC to communicate directly with a device - allowing the PC to efficiently pass commands and data between the system and various expansion devices. Each device must be assigned to a unique address (or address range). Table 13-3 lists the typical I/O port assignments for classic XT and classic AT systems. PS/2 systems use many of the same address assignments, but also add some wrinkles of their own (as shown in Table 13-4). Finally, the I/O scheme for a modern Pentium system (with a 430TX-based motherboard) is listed in Table 13-5.

I/O assignments are generally made manually by setting jumpers or DIP switches on the expansion device itself, or automatically through the use of Plug-and-Play. As with other system resources, it is vitally important that no two devices use the same I/O port(s) at the same time. If one or more I/O addresses overlap, a hardware conflict will result. Commands meant for one device may be erroneously interpreted by another. Keep in mind that while many expansion devices can be set at a variety of addresses, some devices can not.

Memory is another vital resource for the PC. While early devices relied on the assignment of IRQ, DMA channels, and I/O ports, a growing number of modern devices (i.e. SCSI controllers, network cards, video boards, modems, and so on), are demanding memory space for the support of each device’s on-board BIOS ROM. No two ROMs can overlap in their addresses - otherwise, a conflict will occur. Table 13-6 lists a memory map for a modern PC using an Intel 430 or 440 type of chipset (or equivalent).

Now that you’ve got a handle on the way resources are allocated, it’s time to put some of that information to work. Table 13-7 presents a cross-section of typical devices and ports found in today’s PCs, and lists the standard resource assignments most often associated with them - and may assist you in spotting potential conflicts before installing new devices. Note that you may encounter ANY combination of resources listed in the table for a given device.

Fortunately, conflicts are almost always the result of a PC upgrade gone awry. Thus, a technician can be alerted to the possibility of a system conflict by applying the Last Upgrade rule. The rule consists of three parts:

1. A piece of hardware and/or software has been added to the system very recently.
1. The trouble occurred after a piece of hardware and/or software was added to the system.
1. The system was working fine before the hardware and/or software was added.

If all three of these common-sense factors are true, chances are very good that you are faced with a hardware or software conflict. Unlike most other types of PC problems which tend to be specific to the faulty sub-assembly, conflicts usually manifest themselves as much more general and perplexing problems. The following symptoms are typical of serious hardware or software conflicts:

• The system locks up during initialization.
• The system locks up during a particular application.
• The system locks up when a particular device (i.e. a TWAIN scanner) is used.
• The system locks up randomly or without warning regardless of the application.
• The system may not crash, but the device that was added may not function (even though it seems properly configured). Devices that were in the system previously may still work correctly.
• The system may not crash, but a device or application that was working previously no longer seems to function. The newly added device (and accompanying software) may or may not work properly.

What makes these problems so generic is that the severity and frequency of a fault, as well as the point at which the fault occurs, depends on such factors as the particular devices that are conflicting, the resource(s) that are conflicting among the devices (i.e. IRQs, DMAs, or I/O addresses), and the function being performed by the PC when the conflict manifests itself. Since every PC is equipped and configured a bit differently, it is virtually impossible to predict a conflict's symptoms more precisely.

Recognizing the possibility of a conflict is one thing, proving and correcting it is another issue entirely. However, there are some very effective tactics at your disposal. The first rule of conflict resolution is Last In First Out (or LIFO). The LIFO principle basically says that the fastest means of overcoming a conflict problem is to remove the hardware or software that resulted in the conflict. In other words, if you install board X and board Y ceases to function, board X is probably conflicting with the system, so removing board X should restore board Y to normal operation. The same concept holds true for software. If you add a new application to your system, then find that an existing application fails to work properly, the new application is likely at fault. Unfortunately removing the offending element is not enough. You still have to install the new device or software in such a way that it will no longer conflict in the system.

Companion CD: There are several "system reporting tools" on the Companion CD which can help you identify the resources in use (and avoid accidental resource conflicts due to configuration mistakes). Try CONF810E.ZIP, SNOOP330.ZIP, or SYSINF.ZIP on the Companion CD. You may also try some more specific tools like CHKIO.ZIP or IRQINFO.ZIP.

There are two types of software that can cause conflicts in a typical PC; TSRs and device drivers. TSRs (sometimes called popup utilities) loads into memory, usually during initialization, and waits until a system event (i.e. a modem ring or a keyboard "hot key" combination). There are no DOS or system rules that define how such utilities should be written. As a result, many tend to conflict with application programs (and even DOS itself). If you suspect that such a popup utility is causing the problem, find its reference in the AUTOEXEC.BAT file and disable it by placing the command REM in front of its command line (i.e. REM C:\UTILS\NEWMENU.EXE /A:360 /D:3). The REM command turns the line into a "REMark" which can easily be removed later if you choose to restore the line. Remember to reboot the computer so that your changes will take effect.

Device drivers present another potential problem. Most hardware upgrades require the addition of one or more device drivers. Such drivers are called from the CONFIG.SYS file during system initialization (or loaded with Windows), and use a series of command line parameters to specify the system resources that are being used. This is often necessary to ensure that the driver operates its associated hardware properly. if the command line options used for the device driver do not match the hardware settings (or overlap the settings of another device driver) system problems can result. If you suspect that a device driver is causing the problem, find its reference in the CONFIG.SYS file and disable it by placing the command REM in front of its command line (i.e. REM DEVICE = C:\DRIVERS\NEWDRIVE.SYS /A360 /I:5). The REM command turns the line into a "REMark" which can easily be removed later if you choose to restore the line. Remember that disabling the device driver in this fashion will prevent the associated hardware from working, but if the problem clears, you can work with the driver settings until the problem is resolved. Remember to reboot the computer so that your changes will take effect.

Finally, consider the possibility that the offending software has a bug. Try contacting the software manufacturer. There may be a fix or undocumented feature that you are unaware of. There may also be a patch or update that will solve the problem.

A PC user recently added a CD-ROM and adapter board to their system. The installation went flawlessly using the defaults - a 10 minute job. Several days later when attempting to backup the system, the user noticed that the parallel port tape backup did not respond (although the printer that had been connected to the parallel port was working fine). The user tried booting the system from a "clean" bootable floppy disk (no CONFIG.SYS or AUTOEXEC.BAT files to eliminate the device drivers), but the problem remained. After a bit of consideration, the user powered down the system, removed the CD-ROM adapter board, and booted the system from a "clean" bootable floppy disk. Sure enough, the parallel port tape backup started working again.

Stories such as this remind technicians that hardware conflicts are not always the monstrous, system-smashing mistakes that they are made out to be. In many cases, conflicts have subtle, non-catastrophic consequences. Since the CD-ROM was the last device to be added, it was the first to be removed. It took about 5 minutes to realize and remove the problem. However, removing the problem is only part of conflict troubleshooting - re-installing the device without a conflict is the real challenge.

Ideally, the way to correct a conflict would be to alter the conflicting setting. That's dynamite in theory, but another thing in practice. The trick is that you need to know what resources are in use and which ones are free. Unfortunately, there are only two ways to find out. On one hand, you can track down the user manual for every board in the system, then inspect each board individually to find their settings, then work accordingly. This will work (assuming you have the documentation) but it is cumbersome and time-consuming. As an alternative, you can use a resource testing tool such as the Discovery Card (by ForeFront Group). The Discovery Card plugs into a 16-bit ISA slot and uses a series of LEDs to display each IRQ and DMA channel in use. Any LED not illuminated is an available resource. It is then simply a matter of setting your expansion hardware to an IRQ and DMA channel that is not illuminated. Remember that you may have to alter the command line switches of any device drivers. The only resources not illustrated by the Discovery Card are I/O addresses, but since most I/O ports are reserved for particular functions (as you saw in Tables 13-3 to 13-5), you can typically locate an unused I/O port with a minimum of effort.

One of the biggest problems with conflict troubleshooting is that every conflict situation is a bit different. Variations in PC equipment and available resources often reduce conflict troubleshooting to a "hit or miss" process. Fortunately, conflict troubleshooting can be accomplished quickly and easily using the tools provided by Windows 95 (namely the Device Manager). This part of the chapter provides a step-by-step process that you can use for conflict resolution under Windows 95.

NOTE: The steps described below should be read like a flow chart, and you’ll find many references that will take you back and forth to various steps throughout this section.

Start the Device Manager in Windows 95:

1. Click the Start button, then click Settings, then select Control Panel.
1. Double-click the System icon, then click on the Device Manager tab (Fig. 13-1).
1. Make sure "View Devices By Type" is selected.

NOTE: If the hardware that has the conflict isn't visible in the list, click the plus sign (+) next to the type of hardware.

Determine if the device was installed twice. Is the device you were installing (or that suffers from the conflict) listed twice in Device Manager?

• If the device is listed only once, go to Step 2.
• If the device is listed twice, and there is only supposed to be one such device in the system, go to Step 3.
• If the device is listed twice, but there are supposed to be two such devices in the system, go to Step 2.

View the resource settings for the conflicting device:

1. Double-click on the hardware that shows a conflict.
1. In the Device Usage area (such as Fig. 13-2), make sure that there is a check in the box next to the configuration marked "Current". If the box isn't checked, check the box now.
1. Click the Resources tab.

Do you see a box with resource settings (as in Fig. 13-3)?

• If the box with resource settings appears, go to Step 4.
• If the Set Configuration Manually button appears instead, go to Step 5.
• If the device doesn’t have a Resources tab, go to Step 6.

Remove ALL the duplicated device(s), and install again:

1. Remove each duplicate item from the hardware list. Click its name, and then click Remove. When you are finished, no instances of the conflicting hardware should be listed.
1. Click OK.
1. Now (while still within the Control Panel), double-click on the Add New Hardware icon. If you see a message that you already have a wizard open, click Finish in that wizard, and then click the button in this step to start a new wizard.
1. Click Next.
1. Click the option to automatically detect your hardware, and then click Next. Continue until you finish the wizard.

Did this fix the problem?

• If the conflict no longer appears, this should correct the problem, and you should be done. Exit the Control Panel and restart Windows 95.
• If the conflict still appears, go to Step 2.

Identify exactly which resources are causing the conflict:

1. In the Conflicting Device List box, identify the hardware that is using conflicting resources.

Is more than one resource conflict listed?

• If more than one resource conflict is listed, go to Step 7.
• If only one conflict is listed, go to Step 8.
• If no conflicts are listed, or if one or more indications show System Reserved as the conflict, go to Step 9.

Determine why the resources are not displayed:

1. When the Resources tab shows a Set Configuration Manually button, it is either because the device has a conflict or other problem and is disabled, or because the resource settings used by this device are working properly but they don't match any of the known configurations.
1. You can tell which situation applies by reading the text above the button.

Which text message do you see?

• If you see a message which says; "The device is conflicting, or the device is not currently enabled or has a problem", then go to Step 10.
• If you see a message which says; "The resource settings don't match any known configurations.", there is no further solution to the problem. You should probably remove the conflicting device.

You have probably chosen the wrong device. Select the correct device:

1. Click Cancel to return to the hardware list.
1. Carefully double-click the hardware that has a conflict.
1. In the Device Usage area, make sure that there is a check in the box next to the configuration marked "Current". If the box isn't checked, check it now.
1. Click the Resources tab.

Do you see a box with resource settings now?

• If the box with resource settings now appears, go to Step 4.
• If you see a Set Configuration Manually button, go to Step 5.
• If the resource settings still do not appear, there is no further solution to the problem. You should probably remove the conflicting device.

At this point, you should determine just how many devices are listed as being conflicting.

• If you only see one device causing all the conflicts, go to Step 11.
• If more than one device is causing the conflicts, go to Step 12.

Look for a resource setting that doesn't conflict:

1. In the Resource Settings box, double-click the icon next to the resource setting that is conflicting. If you see a message that says "you must clear the Use Automatic Settings box before you can change a resource setting", click OK to close the message, and then clear the Use Automatic Settings box.
1. Scroll through the available resource settings.
1. For each setting, look at the Conflicting Device List box to see if it conflicts with any other hardware.
1. If you find a free setting, click OK.

Did you find a setting that doesn't conflict with any other hardware?

• If you can find a setting which does not conflict, go to Step 13.
• If you cannot find a setting which does not conflict, go to Step 14.
• If you see a message stating that the resource setting cannot be modified, go to Step 15.

If there are no conflicts listed in the Conflicting Device List box, either you are not viewing resources for the correct device, or the conflict has already been resolved (you need to restart your computer to allow Windows 95 to configure the hardware). Look at the top of the dialog box to see if you are viewing resources for the correct device.

There is no further solution to this problem. If restarting Windows 95 does not clear the problem, you may simply need to remove the conflicting device.

Now you need to identify which hardware is conflicting:

1. Click Set Configuration Manually.
1. In the Conflicting Device List box, identify the other hardware that is using the conflicting resources.

Is more than one resource conflict listed?

• If more than one resource conflict is listed, go to Step 16.
• If only one resource conflict is listed, go to Step 17.
• If no conflicts are listed, go to Step 9.

Do you want to disable the device that is causing all the conflicts?

• If you wish to disable the conflicting device, go to Step 18.
• If you must use the hardware that is causing the conflicts, go to Step 17.

Look for resource settings that don't conflict:

1. In the Resource Settings box, double-click the icon next to a resource setting that is conflicting. If you see a message that says "you must clear the Use Automatic Settings box before you can change a resource setting", click OK to close the message, and then clear the Use Automatic Settings box.
1. Scroll through the available resource setting.
1. For each setting, look in the Conflicting Device List box to see if it conflicts with any other hardware.
1. When you find a free setting, click OK.
1. Repeat steps 1 through 4 for each conflicting resource.

Did you find a free setting for each conflicting resource?

• If you do find free settings for each conflicting resource, go to Step 19.
• If some (or all) resources are still conflicting, go to Step 20.
• If you see a message indicating that the resource setting cannot be modified, go to Step 15.

When a free setting is available, change the configuration:

1. Enter the new setting value:
1. Make a note of the old and new settings to refer to later.
1. Click OK. If you see a message prompting you to restart your computer, click No.

NOTE: Depending on the type of hardware you have, you may have to change the jumpers on your hardware card to match the new setting(s), or you may have to run a configuration utility provided by your hardware manufacturer. If the jumper settings on your card aren't set properly, your hardware will not work, even if you resolved the conflict correctly. Refer to your hardware documentation for instructions on changing jumpers.

Restart your computer:

1. Click OK.
1. You may see a message prompting you to restart your computer. Click No.
1. Click the Start button, click Shut Down, and then click Yes.
1. When Windows says it is safe to do so, turn off your computer so you can configure the hardware devices that you’ve changed.

This should correct the problem, and the hardware conflict should now be resolved once the PC is restarted.

Identify hardware you no longer need:

1. Scroll through the available resource settings.
1. When a conflict appears in the Conflicting Device List box, determine whether you still need to use the device that is causing the conflict.

Can you identify a hardware device that you no longer need to use?

• If you can disable the conflicting device, go to Step 21.
• If you cannot disable the conflicting device, go to Step 22.

View the resources for the other device:

1. In the Conflicting Device List box, make a note of which device is using the resource that cannot be modified.
1. Click Cancel.
1. In the hardware list, find and double-click the device that is using the resource.

Does this device have a Resources tab?

• If a Resources tab is available, go to Step 23.
• If a Resources tab is not available, go to Step 24.

How many devices are listed as conflicting?

• If only one device is causing the conflicts, go to Step 11.
• If more than one device is causing the conflicts, go to Step 12.

Look for a resource setting that doesn't conflict:

1. In the Resource Settings box, double-click the icon next to the resource setting that is conflicting. If you see a message that says "you must clear the Use Automatic Settings box before you can change a resource setting", click OK to close the message, and then clear the Use Automatic Settings box.
1. Scroll through the available resource settings.
1. For each setting, look in the Conflicting Device List box to see if it conflicts with any other hardware.
1. If you find a free setting, click OK.

Did you find a setting that doesn't conflict with any other hardware?

• If you manage to find a setting that does not conflict, go to Step 13.
• If you see a message indicating that the resource setting cannot be modified, go to Step 15.
• If all other settings conflict with other hardware, there is no further solution to the problem, and you should probably remove the conflicting device.

Determine how to best disable the conflicting hardware:

1. On the hardware list, double-click the hardware that you want to disable. If you do not see the hardware list, click Cancel until you return to it.
1. In the Device Usage area, click the box next to the configuration marked "Current" to remove the check mark.
1. Click the Resources tab. If there is a Set Configuration Manually button, Windows 95 can disable and free up resources used by this hardware without your removing its card from your computer.

Do you see a Set Configuration Manually button?

• If the button exists, you can effectively disable the device, so go to Step 19.
• If the button is not available, go to Step 25.

Print out a report for each device you changed:

1. In the hardware list, click a device whose resource settings you changed while resolving the conflict. If you do not see the hardware list, click OK until you return to it.
1. Click Print.
1. Click the second option to print the selected class or device.
1. Click OK.
1. Repeat steps 1 through 4 for each device that you changed during this troubleshooting process.

This should correct the problem, and you should be done.

Set resources to conflict with only one device:

1. Double-click a resource that is still conflicting. If you see a message that says "you must clear the Use Automatic Settings box before you can change a resource setting", click OK to close the message, and then clear the Use Automatic Settings box.
1. Scroll through the available resource settings. For each value, write down the setting and the name of the hardware it conflicts with. Then click Cancel.
1. Repeat steps 1 and 2 for each conflicting resource.
1. Looking at the list, see if you can change the resource settings so they conflict with only one device - preferably one you could disable.

Are all conflicts with one device?

• If all the conflicts are with only one device, go to Step 11.
• If resources still conflict with more than one device, there is no further solution to the problem, and you should probably remove the conflicting device.

Determine whether the hardware you want to disable is Plug-and-Play:

1. Select each resource setting that conflicts with the hardware you will disable, and then click OK.
1. When the message appears saying the setting conflicts with another device, click Yes to continue.
1. Click OK until you return to the hardware list.
1. Click the plus sign (+) next to the type of hardware that you want to disable.
1. Double-click the hardware that you want to disable.
1. In the Device Usage area, click the box next to the configuration marked "Current" to remove the check mark.
1. Click the Resources tab.
1. If there is a Set Configuration Manually button, Windows 95 can disable and free up resources used by this hardware without your removing its card from your computer.

Do you see a Set Configuration Manually button?

• If the button exists, you can effectively disable the device, so go to Step 19.
• If the button is not available, go to Step 25.

Write down a list of all devices using resources:

1. Scroll through the resource settings. On a piece of paper, write down the name of each piece of conflicting hardware and its setting.
1. Click Cancel until you return to the hardware list.

Rearrange resource settings for conflicting hardware:

1. On the hardware list, click the plus sign (+) next to the hardware type for the first item on your written list.
1. Double-click the hardware.
1. Click the Resources tab.
1. Double-click the resource setting that you wrote down. If you see a message that says "you must clear the Use Automatic Settings box before you can change a resource setting", click OK to close the message, and then clear the Use Automatic Settings box.
1. Scroll through the available resource settings. For each setting, look in the Conflicting Device List box to see if it conflicts with any other hardware.
1. If you find a free setting other than the one you wrote down, write down the new values, and continue.
1. If you do not find a free setting, repeat steps 1 through 5 until you run out of hardware to try or you find a free setting.

Did you find a free resource setting?

• If you found free resources, go to Step 26.
• If you could not locate free resources, go to Step 27.

Check to see if the device can use a different resource:

1. Click the Resources tab.
1. In the Resource Settings box, double-click the resource setting that you need to free for the other device. If you see a message that says "you must clear the Use Automatic Settings box before you can change a resource setting", click OK to close the message, and then clear the Use Automatic Settings box.
1. Scroll through the available resource settings.
1. For each setting, look in the Conflicting Device List box to see if it conflicts with any other hardware.
1. If you find a free setting, click OK. If you see a message prompting you to restart your computer, click No.

Did you find a free resource setting?

• If Yes, go to Step 28.
• If No (or the settings cannot be modified), go to Step 29.

Decide which device you should disable. Because both devices need to use the same resource setting, you must decide which device you want to use. You must disable and/or remove the other device.

It probably is easier to remove the device that had the original conflict. If you choose to remove the other device, you may see a message telling you that you still have a conflict after completing the procedure. Just restart the procedure and continue resolving the conflict.

Which device would you like to disable?

• If you’d rather disable the original device, go to Step 30.
• If you’d rather disable the other conflicting device, go to Step 31.

Disable the conflicting hardware by removing it:

1. On the hardware list, click the plus sign (+) next to the type of hardware that you want to disable. If you do not see the hardware list, click Cancel until you return to it.
1. Click the hardware you want to disable.
1. Click Remove.

Go to Step 19.

Change the resource settings to utilize the free resources:

1. Save the new setting by clicking OK and then clicking OK again.
1. If you see a message about restarting your computer, click No.
1. Double-click the hardware that first had the conflict.
1. Click the Resources tab.
1. Double-click the resource that is conflicting. If you see a message that says "you must clear the Use Automatic Settings box before you can change a resource setting", click OK to close the message, and then clear the Use Automatic Settings box.
1. Change the resource setting to the value you just freed. The Conflicting Device List box may show a conflict with the other hardware that you just changed.
1. Click OK. If you see a message, click Yes to continue.

Go to Step 19.

You must disable some hardware to relieve the conflict. Do you want to disable the hardware that caused the original conflict?

• If you want to disable the hardware that originally caused the conflict, go to Step 18.
• If you must use ALL of the hardware in the system, there is no further solution to the problem since the conflict cannot be resolved.

Determine whether there are any remaining conflicts:

1. Click OK to return to the hardware list.
1. Double-click the device that had the original conflict.
1. Click the Resources tab.
1. See if there are any remaining conflicts listed in the Conflicting Device List box.

NOTE: If the conflict you just resolved is listed, you can ignore it. It will no longer conflict after you restart your computer later.

Are there still conflicts listed?

• If all the resources are now set without any conflicts, go to Step 19.
• If some or all of the resources are still conflicting, go to Step 20.

You must decide which device to disable. Because both devices need to use the same resource setting, you must decide which device you want to use. You must disable and remove the other device.

It probably is easier to remove the device that had the original conflict at this point. If you choose to remove the other device, you may see a message telling you that you still have a conflict after you finish and restart your computer. Just restart this procedure and continue resolving the conflict.

Which device would you like to disable?

• If you choose to disable the device with the original conflict, go to Step 30.
• If you choose disable the other device that it is conflicting with, go to Step 31.

Determine whether you have to remove the card to disable the hardware:

1. On the hardware list, double-click the hardware that you want to disable. If you do not see the hardware list, click Cancel until you return to it.
1. In the Device Usage area, make sure that there is a check in the box next to the configuration marked "Current". If the box isn’t checked, check it now.
1. Click the Resources tab. If there is a Set Configuration Manually button, Windows 95 can free up resources for this hardware without your removing its card from your computer.

When you see a Set Configuration Manually button:

If you do see that button, and there are no resource settings listed in the box, you’ll need to restart your computer.

1. Click OK, and then click OK again.
1. You may be prompted to restart your computer. Click Yes.

When you don’t see a Set Configuration Manually button:

If no button is available, you’ll need to disable the physical hardware by removing it from the system.

1. On the hardware list, click the plus sign (+) next to the type of hardware that you want to disable. If you do not see the hardware list, click Cancel until you return to it.
1. Click the hardware you want to disable.
1. Click Remove, and then click OK.
1. You may be prompted to restart your computer. You will have to remove the card for this hardware from your computer, so you need to shut down instead of restarting. Click No.
1. Click the Start button, click Shut Down, and then click Yes. When the message says it is safe to do so, turn off your computer and remove the card from your computer.
1. Restart your PC and check if your problem has been resolved.

This should correct the conflict, and complete your troubleshooting procedure.

Determine whether you have to remove the card to disable the hardware:

1. On the hardware list, double-click the hardware that you want to disable. If you do not see the hardware list, click Cancel until you return to it.
1. In the Device Usage area, click the box next to the configuration marked "Current" to remove the check mark.
1. Click the Resources tab. If there is a Set Configuration Manually button, Windows 95 can free up resources for this hardware without your removing its card from your computer.

Do you see a Set Configuration Manually button?

• If you see the button, go to Step 32.
• If you don’t see the button, go to Step 33.

Determine whether there are any remaining conflicts:

1. Click OK to return to the hardware list.
1. Double-click the device that had the original conflict.
1. Click the Resources tab.
1. See if there are any remaining conflicts listed in the Conflicting Device List box. If the conflict you just resolved is listed, you can ignore it. It will no longer conflict after you restart your computer later.

Are there still conflicts listed?

• If there are no further conflicts, go to Step 19.
• If one or more conflicts are still listed, go to Step 34.

Disable hardware by removing it:

1. On the hardware list, click the plus sign (+) next to the type of hardware that you want to disable. If you do not see the hardware list, click Cancel until you return to it.
1. Click the hardware you want to disable.
1. Click Remove.

Go to Step 19.

Try setting resources to conflict with only one device:

1. Double-click a resource that is still conflicting. If you see a message that says "you must clear the Use Automatic Settings box before you can change a resource setting", click OK to close the message, and then clear the Use Automatic Settings box.
1. Scroll through the available resource settings. For each value, write down the setting and the name of the hardware it conflicts with, then click Cancel.
1. Repeat steps 1 and 2 for each conflicting resource.
1. Looking at the list, see if you can change the resource settings so they conflict with only one device - preferably one you could disable.

Are all conflicts now with one device?

• When all the conflicts are with only one device, go to Step 11.
• If the resources still conflict with more than one device (or cannot be changed), there is no further solution to this problem, and you should probably remove the conflicting device.

Traditional PCs used devices that required manual configuration - each IRQ, DMA, I/O port, and memory address space had to be specifically set through jumpers on the particular device. If you accidentally configured two or more devices to use the same resource, a conflict would result. This would require you to isolate the offending device(s), identify available resources, and reconfigure the offending device(s) manually. Taken together, this was often a cumbersome and time-consuming process.

In the early 1990s, PC designers realized that it was possible to automate the process of resource allocation each time the system initializes. This way, a device need only be installed, and the system would handle its configuration without the assistance or intervention of the installer. This concept became known as "Plug-and-Play" (PnP), and is now standard in the PC arena. PnP systems require three elements in order to function:

• PnP-compliant devices (such as video boards, modems, drive controllers, and so on).
• PnP-compliant BIOS (now used in all Pentium-class systems).
• PnP-compliant operating systems (like Windows 95).

When the PnP system works properly, a PnP device can be installed in an available expansion slot on a PnP-supported motherboard (with a PnP BIOS). When Windows 95 starts, it recognizes the new PnP device, assigns resources, then attempts to install the proper protected-mode driver (which could be installed from manufacturer’s floppy disk or a Windows 95 installation CD). Thereafter, the system "remembers" the new device, and reconfigures it each time the system starts. Ideally, if the PnP device is ever removed, Windows 95 would automatically clear the device from its "system", and free the resources for other devices.

However, if any of these elements are missing, devices will not be "auto-configured". For example, PnP won’t work under DOS (though there are DOS PnP drivers which can be used to initialize PnP devices). Older, jumper-configured devices (called legacy devices) also won’t support PnP, and resources need to be reserved for legacy devices in order to prevent the PnP system from ignoring them entirely.

NOTE: PnP "auto-configuration" information is stored in the Extended System Configuration Data (ESCD) area, and is cleared when the CMOS RAM is cleared or lost.

Once you have determined the IRQ, DMA, and I/O settings that are in use, a thorough technician will note each setting on paper, then tape the notes inside the system's enclosure. This extra step will greatly ease future expansion and troubleshooting. To make your note taking process even faster, you can photocopy and use the System Setup Form included in the Appendix of this book.

That concludes Chapter 13. Be sure to review the glossary and chapter questions on the accompanying CD. If you have access to the Internet, take some time to review a few of the resources listed below:

Data Depot: http://www.datadepo.com/datadepo.htm

Download MSD 2.11: http://support.microsoft.com/download/support/mslfiles/GA0363.EXE

The Discovery Card: http://www.ffg.com/pcproducts/discover.html

Windsor Technologies: http://www.windsortech.com/