APC_INDEX_MISMATCH is a Windows Blue Screen of Death (BSOD) error with the bug check value:

0x00000001

Microsoft defines APC_INDEX_MISMATCH as a mismatch in the Asynchronous Procedure Call (APC) state index. In practical terms, Windows detected an inconsistency in how kernel-level code—most commonly a device driver or file-system component—managed APC operations.

A typical blue screen may display:

Your device ran into a problem and needs to restart.

Stop code: APC_INDEX_MISMATCH

The system then restarts automatically.

Although users sometimes assume that any BSOD means defective RAM, motherboard, or another hardware component, APC_INDEX_MISMATCH is frequently associated with drivers and kernel-level software rather than an immediate indication of hardware failure.

Understanding APC and APC_INDEX_MISMATCH

APC stands for Asynchronous Procedure Call.

Windows uses APC mechanisms to execute code asynchronously in the context of a particular thread.

Kernel-mode drivers must correctly manage operations that disable and re-enable APC delivery. Microsoft states that a common cause of APC_INDEX_MISMATCH is a file system or driver having a mismatched sequence of calls that disable and re-enable APCs.

For example, a kernel driver may effectively perform an operation similar to:

Disable APC → perform operation → enable APC

If the driver disables APC processing but fails to restore it correctly—or restores it more times than it should—the kernel can detect the inconsistent state.

Windows deliberately stops the system because continuing with corrupted kernel state could produce unpredictable results.

APC_INDEX_MISMATCH Bug Check Parameters

The bug check code is:

0x00000001

Its parameters can provide useful information during crash-dump analysis.

Parameter 1

Address of the system function/system call or worker routine.

Parameter 2

Value of the current thread's ApcStateIndex field.

Parameter 3

Value of the current thread's CombinedApcDisable field.

This field contains information relating to:

• SpecialApcDisable
• KernelApcDisable

According to Microsoft, a negative value can indicate that APCs were disabled without being properly re-enabled, while a positive value can indicate that APCs were enabled too many times.

Parameter 4

Indicates the call type:

0 = System call

1 = Worker routine

These parameters are primarily useful to administrators, developers, and engineers analyzing memory dumps with WinDbg.

Common Causes of APC_INDEX_MISMATCH

1. Faulty or Incompatible Device Driver

Drivers are among the first things to investigate.

Possible offenders include:

• Audio drivers
• Graphics drivers
• Printer drivers
• Webcam drivers
• USB drivers
• Bluetooth drivers
• Wi-Fi/Ethernet drivers
• Storage controller drivers
• Chipset drivers
• Virtual-device drivers
• Security software drivers

The problem may start immediately after installing or updating a device.

2. Recently Updated Driver

A newer driver is not automatically a better driver.

For example, suppose Windows Update installs a newer audio driver and APC_INDEX_MISMATCH starts immediately afterward.

In this situation, rolling back the driver may be more effective than attempting another update.

3. Corrupted Driver Installation

Driver files or associated configuration can become damaged because of:

• Interrupted updates
• Forced shutdowns
• Failed installations
• Disk corruption
• Improper driver removal
• Third-party driver utilities

A clean reinstall may resolve the problem.

4. Audio Drivers

Audio drivers operate close to the Windows kernel and can therefore be involved in BSOD conditions.

If APC_INDEX_MISMATCH happens while:

• Playing audio
• Connecting a headset
• Starting a meeting
• Using a microphone
• Starting recording software
• Opening a communication application

investigate the audio driver.

Common devices may use drivers from Realtek, Intel, AMD, NVIDIA, USB-audio manufacturers, or the PC manufacturer's customized audio package.

5. Webcam or Camera Drivers

If the computer crashes when you:

• Start the camera
• Join a video meeting
• Enable video conferencing
• Open the Camera application
• Switch cameras

the camera/webcam driver should be investigated.

USB webcams can also involve USB controller drivers.

6. Printer Drivers

Printer drivers and print-related Windows components have historically been capable of triggering kernel crashes.

Microsoft previously documented a Windows issue in which printing from certain applications could produce APC_INDEX_MISMATCH. That specific historical issue was addressed through Windows updates, illustrating why Windows servicing status matters when troubleshooting this stop code.

If the BSOD occurs specifically when printing, investigate:

• Printer driver
• Print software
• Print processor
• Old printer packages
• Windows updates

7. Windows Update Problems

If APC_INDEX_MISMATCH started immediately after a Windows update, the update may have introduced:

• Driver compatibility problems
• Kernel changes exposing an old driver bug
• Printer compatibility problems
• Hardware-driver conflicts

Check:

Settings → Windows Update → Update history

Determine exactly what changed before the first crash.

8. Third-Party Antivirus or Security Software

Antivirus, endpoint protection, encryption, VPN, DLP, firewall, and security-monitoring software frequently install kernel-level drivers.

These drivers may interact with:

• File system operations
• Network traffic
• Process creation
• Memory
• USB devices
• Storage
• Encryption

Temporarily removing a suspected third-party security package can therefore be useful during controlled troubleshooting.

Simply disabling its interface may not unload its kernel driver, so uninstalling the software may occasionally be necessary for a meaningful test.

9. Corrupted Windows System Files

Damaged Windows components can contribute to system instability.

Common causes include:

• Failed updates
• Unexpected shutdowns
• Storage errors
• Malware
• File-system corruption

Windows includes DISM and System File Checker for checking and repairing system components.

10. BIOS, Firmware or Chipset Problems

Outdated BIOS/UEFI firmware or chipset drivers can sometimes contribute to low-level stability problems.

This is especially worth investigating if:

• Windows was recently upgraded
• CPU or motherboard hardware changed
• BIOS settings were modified
• New RAM was installed
• New PCIe hardware was installed
• The manufacturer's BIOS release notes mention stability or compatibility fixes

11. RAM or Hardware Instability

APC_INDEX_MISMATCH usually directs attention toward software/driver problems first, but hardware should not be completely ignored.

Potential hardware-related factors include:

• Defective RAM
• Unstable overclock
• CPU instability
• Storage corruption
• Motherboard issues
• Unstable XMP/EXPO memory profile

Hardware becomes more suspicious if the computer generates many different BSOD codes rather than consistently producing APC_INDEX_MISMATCH.

How to Fix APC_INDEX_MISMATCH

Solution 1: Restart and Determine Whether the Error Repeats

One isolated BSOD does not necessarily indicate a persistent problem.

After restarting, note:

• What application was running?
• Was the webcam active?
• Were you printing?
• Was audio playing?
• Was a USB device connected?
• Did Windows just install updates?
• Was a driver recently updated?

The activity immediately before the crash can provide an important clue.

Solution 2: Install Windows Updates

Open:

Settings → Windows Update

Select:

Check for updates

Install applicable security and quality updates and restart Windows.

Also inspect:

Windows Update → Update history

This helps determine whether the problem started after a specific update.

Solution 3: Update Device Drivers

Do not randomly update every driver unless necessary.

Concentrate first on drivers related to the activity occurring during the crash.

Open Device Manager:

Win + X → Device Manager

Check important categories such as:

• Display adapters
• Sound, video and game controllers
• Cameras
• Network adapters
• Bluetooth
• Storage controllers
• Universal Serial Bus controllers
• Printers

For critical drivers, downloading the appropriate package from the PC or hardware manufacturer's support site is generally preferable to using unknown third-party driver-update utilities.

Solution 4: Roll Back a Recently Updated Driver

If the problem started after a driver update:

1. Open Device Manager.
2. Locate the affected device.
3. Right-click it.
4. Select Properties.
5. Open the Driver tab.
6. Select Roll Back Driver, if available.
7. Restart Windows.

If Roll Back Driver is unavailable, uninstalling the driver and installing a known-good OEM version may be necessary.

Solution 5: Reinstall the Suspected Driver

If updating does not work, perform a clean driver reinstall.

For example:

1. Download the correct driver from the manufacturer.
2. Open Device Manager.
3. Locate the device.
4. Right-click it.
5. Select Uninstall device.
6. Restart Windows.
7. Install the downloaded driver.
8. Restart again.

For graphics drivers and certain complex devices, use the manufacturer's recommended clean-install procedure where available.

Solution 6: Repair Windows with DISM

Open Command Prompt or Terminal as Administrator.

Run:

DISM /Online /Cleanup-Image /RestoreHealth

Allow the process to complete.

DISM checks and repairs the Windows component store used by Windows servicing and System File Checker.

Restart the computer if repairs are performed.

Solution 7: Run System File Checker

After DISM completes, run:

sfc /scannow

Wait until verification reaches 100%.

Possible results include:

Windows Resource Protection did not find any integrity violations.

or

Windows Resource Protection found corrupt files and successfully repaired them.

Restart Windows after repairs.

Solution 8: Check Event Viewer

Event Viewer may provide clues about what happened immediately before the crash.

Press:

Win + R

Enter:

eventvwr.msc

Navigate to:

Windows Logs → System

Look for Critical/Error events around the exact BSOD time.

Pay particular attention to events involving:

• Drivers
• Disk
• NTFS
• WHEA
• Kernel-Power
• Device initialization
• Service failures

Note that Kernel-Power Event ID 41 often records that Windows restarted unexpectedly; it does not by itself identify the underlying cause.

Solution 9: Use Reliability Monitor

Reliability Monitor provides a convenient timeline of application and Windows failures.

Press:

Win + R

Enter:

perfmon /rel

Look for red failure icons around the time APC_INDEX_MISMATCH occurred.

Check:

• Windows failures
• Application failures
• Driver installations
• Windows updates
• Hardware errors

The timeline can help correlate a newly installed component with the beginning of the crashes.

Solution 10: Check the Windows Minidump Folder

Windows commonly stores crash dump files in:

C:\Windows\Minidump

You may see files similar to:

082926-14531-01.dmp

A larger dump may also exist at:

C:\Windows\MEMORY.DMP

Crash dumps are considerably more useful than simply searching for the filename displayed on a blue screen.

Solution 11: Analyze the Crash with WinDbg

For advanced troubleshooting, use Microsoft's Windows debugger.

Microsoft specifically recommends debugger analysis for APC_INDEX_MISMATCH and notes that the !analyze debugger extension can help determine the root cause. The !apc extension can also display APC information.

Open the dump and execute:

!analyze -v

Look for information such as:

BUGCHECK_CODE
MODULE_NAME
IMAGE_NAME
FAILURE_BUCKET_ID
STACK_TEXT

If a third-party .sys driver repeatedly appears in multiple crashes, investigate that driver.

Important: ntoskrnl.exe Is Not Automatically the Culprit

BSOD analysis utilities sometimes report:

ntoskrnl.exe

This does not automatically mean that the Windows kernel itself is defective.

The kernel may simply be where Windows detected corruption caused earlier by another driver.

Therefore, do not replace Windows or assume ntoskrnl.exe itself is the root cause solely because it appears in the dump.

Look at the complete call stack and repeated crash patterns.

Solution 12: Boot Windows in Safe Mode

Safe Mode loads Windows with a reduced set of drivers and services.

If the computer becomes stable in Safe Mode, this increases suspicion of:

• Third-party driver
• Startup software
• Security software
• Hardware utility
• Background service

You can access recovery options through:

Settings → System → Recovery → Advanced startup

Then navigate through the troubleshooting/startup settings options to start Safe Mode.

Solution 13: Perform a Clean Boot

A clean boot can help identify conflicts caused by third-party services or startup applications.

Press:

Win + R

Enter:

msconfig

Open the Services tab.

Select:

Hide all Microsoft services

Then disable the remaining third-party services for testing.

Also disable unnecessary startup applications through Task Manager.

Restart the computer.

If the BSOD disappears, re-enable items gradually until the problematic software is identified.

Solution 14: Check RAM

Press:

Win + R

Enter:

mdsched.exe

Select:

Restart now and check for problems

Windows Memory Diagnostic will test the memory.

For intermittent or difficult RAM problems, longer dedicated memory testing may be required.

Solution 15: Check the System Drive

Open Terminal/Command Prompt as Administrator and run:

chkdsk C: /scan

This performs an online scan of the Windows volume.

If Windows reports problems requiring offline repair, follow the recommended repair procedure.

Before performing disk repairs, ensure important data is backed up.

Solution 16: Check SSD/HDD Health

If APC_INDEX_MISMATCH occurs together with:

• Disk errors
• Freezing
• File corruption
• Very slow boot
• Missing files
• Multiple unrelated BSOD codes

check the storage device's health.

Use the SSD/HDD manufacturer's diagnostic software where available.

A failing storage device can corrupt Windows or driver files and indirectly produce BSODs.

Solution 17: Update BIOS/UEFI

Check your computer or motherboard manufacturer's support page for a newer BIOS/UEFI release.

Before updating:

• Verify the exact model.
• Confirm the BIOS version.
• Read the manufacturer's instructions.
• Keep AC power connected.
• Do not interrupt the update.

Incorrect firmware flashing can prevent the computer from booting, so BIOS updates should be performed carefully.

Solution 18: Update Chipset and Platform Drivers

Install current OEM-supported versions of:

• Chipset driver
• Intel/AMD platform components
• Management Engine/platform-management components where applicable
• Storage controller drivers
• Serial IO drivers
• USB controller components

Laptop users should generally begin with the laptop manufacturer's support page because OEM systems may require customized drivers.

Solution 19: Remove Recently Added Hardware

If the error began after installing hardware such as:

• USB adapter
• Webcam
• Printer
• Sound device
• Wi-Fi adapter
• PCIe card
• Docking station

disconnect the device temporarily.

If the system becomes stable, reinstall or update the associated driver before reconnecting it.

Solution 20: Temporarily Remove Third-Party Security Software

For diagnostic purposes, temporarily uninstall recently installed:

• Antivirus
• Endpoint protection
• VPN
• Firewall
• Encryption software
• Anti-cheat software
• System-monitoring tools

Restart and test.

If the BSOD stops, install an updated compatible version or contact the vendor.

Ensure the computer remains appropriately protected while performing this test.

Solution 21: Disable Overclocking

Return CPU, GPU and memory settings to their default specifications.

Temporarily disable:

• CPU overclock
• GPU overclock
• RAM overclock
• XMP/EXPO profiles
• Undervolting
• Aggressive performance tuning

An unstable system can generate misleading driver-related crashes.

Solution 22: Use System Restore

If APC_INDEX_MISMATCH started recently and a restore point exists:

Press:

Win + R

Enter:

rstrui.exe

Select a restore point created before the problem started.

System Restore can revert drivers, registry changes, updates and system configuration without normally affecting personal documents.

Solution 23: Uninstall a Problematic Windows Update

If the crashes began immediately after a Windows update, check:

Settings → Windows Update → Update history

If evidence strongly points to a particular update, uninstalling it temporarily may be appropriate.

However, removing security updates should not be the first troubleshooting step and should generally be temporary while identifying the actual compatibility problem.

Solution 24: Use Driver Verifier – Advanced Users Only

Windows includes Driver Verifier, which can stress-test kernel drivers and expose defective behavior.

Run:

verifier

However, Driver Verifier is an advanced diagnostic tool.

It can intentionally trigger additional BSODs when a problematic driver is detected.

Do not enable every possible test without understanding the consequences, particularly on production servers or business-critical computers.

Ensure you know how to enter Safe Mode or Windows Recovery Environment before enabling it.

To reset Driver Verifier from an elevated Command Prompt:

verifier /reset

Restart Windows afterward.

Recommended Troubleshooting Order

For most users, use this order:

1. Note what was happening when the BSOD occurred.
2. Check Windows Update history.
3. Check recently installed or updated drivers.
4. Update or roll back suspected drivers.
5. Run DISM.
6. Run SFC.
7. Check Reliability Monitor.
8. Check Event Viewer.
9. Analyze minidump files.
10. Test in Safe Mode.
11. Perform a clean boot.
12. Test RAM.
13. Check storage health.
14. Update BIOS/chipset drivers if appropriate.
15. Use Driver Verifier only when necessary.
16. Consider System Restore or Windows repair if the issue remains unresolved.

Commands Useful for APC_INDEX_MISMATCH Troubleshooting

Repair Windows image

DISM /Online /Cleanup-Image /RestoreHealth

Check system files

sfc /scannow

Scan system drive

chkdsk C: /scan

Open Device Manager

devmgmt.msc

Open Event Viewer

eventvwr.msc

Open Reliability Monitor

perfmon /rel

Windows Memory Diagnostic

mdsched.exe

System Restore

rstrui.exe

Driver Verifier

verifier

Disable Driver Verifier

verifier /reset

For IT Administrators: How to Diagnose Repeated APC_INDEX_MISMATCH Crashes

If you manage multiple computers, avoid treating every APC_INDEX_MISMATCH as an isolated Windows problem.

Compare affected systems for common factors.

For example:

PC 1: Realtek audio driver version X
PC 2: Realtek audio driver version X
PC 3: Realtek audio driver version X

If all three started crashing after the same driver deployment, that common driver becomes a strong suspect.

Correlate:

• Windows build
• Driver versions
• BIOS versions
• Hardware model
• Antivirus version
• Recently deployed software
• Windows update history
• Crash timestamp
• Dump-file stack
• Failure bucket

This approach is particularly useful in corporate environments.

For Driver Developers

Microsoft describes APC_INDEX_MISMATCH as an internal kernel error that can occur when leaving a system call. One possible programming cause is an incorrectly matched sequence when entering and leaving guarded or critical regions. For example, a call to KeEnterCriticalRegion needs the corresponding KeLeaveCriticalRegion.

Driver developers should therefore inspect code involving:

• Critical regions
• Guarded regions
• APC disable counts
• Thread state
• Kernel APC handling

Microsoft also points driver developers toward Static Driver Verifier and its CriticalRegions rule for detecting improper sequences in driver source code.

Frequently Asked Questions (FAQ)

1. What does APC_INDEX_MISMATCH mean?

It means Windows detected an inconsistency in the APC state maintained by a thread. The official bug check value is 0x00000001.

2. Is APC_INDEX_MISMATCH a hardware problem?

Not necessarily.

Device drivers and kernel-level software should generally be investigated first. Hardware testing becomes more important if you also experience other random BSOD codes, memory errors, freezes, disk corruption, or instability.

3. Can a driver cause APC_INDEX_MISMATCH?

Yes. Driver or file-system code that incorrectly manages APC-related state is a primary cause identified by Microsoft.

4. Can a printer cause APC_INDEX_MISMATCH?

Printer drivers or Windows printing components can be involved. Microsoft has previously fixed a Windows issue that could cause APC_INDEX_MISMATCH when printing from certain applications.

If the crash happens only while printing, investigate the printer driver and Windows update status first.

5. Can an audio driver cause this BSOD?

Yes. Audio drivers operate in areas where faulty kernel-mode code can cause system crashes.

If the error happens while playing sound, connecting a headset, or starting voice/video software, update or reinstall the audio driver.

6. Can a webcam cause APC_INDEX_MISMATCH?

Potentially.

If the BSOD consistently occurs when the camera activates, investigate the webcam driver, USB controller driver and related video-conferencing software.

7. Why does ntoskrnl.exe appear in my crash report?

ntoskrnl.exe is the Windows kernel.

Its presence in a crash report does not automatically mean it caused the original problem. Windows may have detected corruption caused by another kernel-mode driver.

A complete dump analysis is needed.

8. Where are BSOD dump files stored?

Common locations include:

C:\Windows\Minidump

and:

C:\Windows\MEMORY.DMP

The exact dump configuration depends on Windows startup and recovery settings.

9. How can I identify which driver caused APC_INDEX_MISMATCH?

Analyze the dump using WinDbg and begin with:

!analyze -v

Microsoft specifically recommends WinDbg analysis for this bug check.

Look for third-party driver names and repeated patterns across multiple dumps.

10. Should I reinstall Windows immediately?

Usually no.

First investigate:

• Drivers
• Windows updates
• System files
• Recent software
• Crash dumps
• RAM
• Storage
• BIOS/firmware

Reinstalling Windows should generally be considered only after reasonable diagnostic steps fail.

11. Will SFC fix APC_INDEX_MISMATCH?

SFC may help if corrupted Windows system files contribute to the problem, but it will not repair a defective third-party driver.

Use:

sfc /scannow

It is often useful to run DISM beforehand.

12. Should I use Driver Verifier?

Only if normal troubleshooting and crash-dump analysis have not identified the problematic driver.

Driver Verifier can deliberately cause BSODs when it detects improper driver behavior, so it should be used carefully.

13. How do I disable Driver Verifier if Windows starts crashing?

Boot into Safe Mode or Windows Recovery if necessary and run an elevated Command Prompt:

verifier /reset

Restart Windows.

14. Can Windows Update fix APC_INDEX_MISMATCH?

Yes, when the underlying problem is a Windows bug or a compatibility issue corrected by an update.

Windows Update can also deliver newer drivers, although OEM drivers may sometimes be preferable.

15. What should I do if APC_INDEX_MISMATCH happens repeatedly?

Do not repeatedly restart the computer without investigating.

Collect:

• Minidump files
• Windows version/build
• Driver versions
• Event Viewer information
• Reliability Monitor history
• Details about what was happening at crash time

Repeated crashes provide valuable diagnostic evidence.

Conclusion

APC_INDEX_MISMATCH (Bug Check 0x00000001) is a Windows kernel-level BSOD indicating an inconsistency in the Asynchronous Procedure Call state. Microsoft identifies mismatched APC disable/re-enable operations in file-system or driver code as a common underlying cause.

For most computers, troubleshooting should begin with recent driver and Windows changes, especially audio, graphics, printer, webcam, USB, network, chipset, storage, security, and other kernel-level software.

The most effective troubleshooting sequence is generally:

Check recent changes → update/rollback drivers → repair Windows files → review Event Viewer/Reliability Monitor → analyze minidumps → test Safe Mode/clean boot → test hardware → perform advanced driver debugging if required.

For recurring APC_INDEX_MISMATCH errors, analyzing the actual .dmp file is far more reliable than guessing from the stop-code name alone.

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