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APC_INDEX_MISMATCH is Windows 10 stop code 0x00000001, a kernel-level consistency failure usually caused by a driver or file-system component making an unmatched asynchronous procedure-call (APC) disable/re-enable call. To stop the blue screen, first record the crash details, undo recent driver or hardware changes in Safe Mode, update Windows and firmware, test memory, and collect a dump if the failure continues. Use System Restore or Windows Recovery Environment before considering a reset or clean installation.
What does APC_INDEX_MISMATCH mean?
Microsoft defines bug check 0x00000001 as an APC index mismatch. An APC lets kernel-mode code queue work for a thread. Drivers and file-system components must balance calls that disable and re-enable APC delivery; when the sequence does not balance, Windows detects an invalid kernel state and halts to protect data.
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Microsoft identifies a mismatched sequence of APC disable and re-enable calls as the most common mechanism. A positive or negative CombinedApcDisable value can show that APCs were enabled too many times or were not re-enabled. The stop code identifies the type of consistency failure, not necessarily the exact driver responsible.
What usually triggers the mismatch?
- A recently installed, rolled-back, or partially updated third-party driver.
- Graphics, network, storage, USB, audio, or chipset drivers that run in the kernel.
- Antivirus, VPN, backup, encryption, or other security filter drivers.
- New RAM, a peripheral, firmware, BIOS settings, or another hardware change.
- Corrupted Windows components or memory errors that make a driver appear to be at fault.
In Microsoft’s 2026 general stop-error analysis, third-party drivers accounted for 70 percent of cases, hardware 10 percent, Microsoft code 5 percent, and 15 percent were unclassified because memory was too corrupted. Those figures describe Microsoft’s overall stop-error population, not a guarantee about this particular crash.
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What should I record before changing Windows?
Capturing evidence before uninstalling software or replacing hardware gives you a way to identify the trigger and to reverse changes if the crash returns.
- Photograph the entire blue screen. Include the exact spelling of
APC_INDEX_MISMATCH, any “What failed” filename such as a.sysmodule, and whether a percentage counter or restart message appeared. - Write a change timeline. Note the first crash and anything installed immediately beforehand: a Windows update, graphics/network/storage driver, antivirus or VPN filter, peripheral, RAM, BIOS update, or other hardware.
- Check the System log. Open Event Viewer, choose Windows Logs > System, and inspect entries at the crash time. Look for driver, service, disk, firmware, or unexpected-shutdown events that line up with the blue screen.
- Preserve existing dumps. Do not use cleanup software or delete
%SystemRoot%Minidumpor%SystemRoot%MEMORY.DMPuntil you have copied any files you may need.
A named module is a lead, not proof. A driver can be blamed because it was the first component detected after memory corruption elsewhere.
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Safe Mode starts Windows with a minimal set of drivers, making it useful when normal startup immediately blue-screens. Remove or roll back the newest kernel-level change before making broad system changes.
Enter Safe Mode from a working session
- Open Settings > Update & Security > Recovery.
- Under Advanced startup, select Restart now.
- After the restart, choose Troubleshoot > Advanced options > Startup Settings > Restart.
- At the numbered menu, press 4 for Safe Mode or 5 for Safe Mode with Networking. Use networking only when you need an online vendor page.
Enter Safe Mode when Windows will not stay open
Interrupt normal startup by powering off during boot two or three times; Windows should open the Windows Recovery Environment (WinRE). Choose See advanced repair options > Troubleshoot > Advanced options > Startup Settings > Restart, then select Safe Mode. If automatic recovery does not appear, use a Windows recovery drive or installation USB to reach Repair your computer.
Undo the latest driver or utility
- In Safe Mode, right-click Start and open Device Manager.
- Expand the category related to the change, such as Display adapters, Network adapters, Storage controllers, Sound, video and game controllers, or Universal Serial Bus controllers.
- Open the device’s Properties, select the Driver tab, and use Roll Back Driver when it is available.
- If rollback is unavailable, choose Uninstall Device. Select the option to remove the driver package only when you are certain it is the newly installed package, then restart and install a known-good release from the computer or component manufacturer.
- For a recently installed kernel-level utility, uninstall it from Settings > Apps > Apps & features (or Control Panel > Programs and Features) and restart.
Disconnect a newly added peripheral while testing. If the blue screen stops, reconnect one device at a time so you can identify the trigger.
Which Windows, driver, BIOS, and firmware updates should I install?
After removing a suspect change, bring the remaining platform components to compatible versions. A fix can fail if Windows is current but the OEM BIOS or storage firmware is not.
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- Open Settings > Update & Security > Windows Update, select Check for updates, install available quality updates, and then check View optional updates for applicable driver packages.
- For graphics, Wi-Fi, audio, chipset, storage, and laptop-specific devices, compare the installed version in Device Manager with the version on your PC or component manufacturer’s support page. Prefer the package intended for your exact model and Windows 10 edition.
- Install BIOS and firmware only from the system or component manufacturer. Keep AC power connected, do not interrupt the flash process, and follow that vendor’s recovery instructions.
- If no vendor update exists, Microsoft’s advanced guidance allows disabling the related service as a diagnostic or temporary measure. Record the original startup setting so you can restore it.
Windows 10 support ended on October 14, 2025. Microsoft no longer provides free Windows Update software updates, technical assistance, or security fixes for Windows 10. Separately from repairing this crash, check whether the PC can move to a supported Windows release or whether the hardware needs replacement.
How do I test RAM for APC_INDEX_MISMATCH?
A memory fault can corrupt kernel data and create misleading driver symptoms. A clean test reduces the likelihood of defective RAM but does not rule out a driver.
- Press Windows key + R, type
mdsched, and press Enter. - Choose Restart now and check for problems. Save open work first; the diagnostic reboots immediately.
- Let the test complete through its reboot. If errors appear, power off, reseat modules if your manufacturer permits it, test one module at a time, and replace the failing part or have the system serviced.
- If Windows does not show the result, open Event Viewer and go to Applications and Services Logs > Microsoft > Windows > MemoryDiagnostics-Results > Debug. Event ID 2001 means no memory errors were detected.
Run the test again after changing memory settings or installing a module. A passing result cannot validate a suspect driver, firmware component, or motherboard slot.
How do I collect and read a crash dump?
A dump preserves the kernel state at the stop, which is more useful than guessing from the stop-code name alone.
Enable an automatic memory dump
- Open Control Panel > System and Security > System, then select Advanced system settings.
- On the Advanced tab, under Startup and Recovery, select Settings.
- Under Write debugging information, choose Automatic memory dump. Confirm that the system drive has enough free space and that Automatically restart is disabled if you need time to read the blue screen.
- Restart. A complete automatic dump is normally written to
%SystemRoot%MEMORY.DMP; small dumps are stored in%SystemRoot%Minidump.
Inspect the dump in WinDbg
Open the dump in WinDbg, allow symbols to load, and begin with !analyze -v. Review the reported process, stack, and suspected module rather than treating the “Probably caused by” line as conclusive. When APC state is relevant, !apc can show APC information for the current thread. Save the dump and analysis output before making another change.
Driver Verifier can expose faulty driver behavior, but Microsoft warns that it can cause additional crashes. Use it only after preserving a dump and only when you know how to return to Safe Mode and run verifier /reset or disable the selected checks from recovery.
Can System Restore or WinRE repair the crash without deleting my files?
Yes. If the crashes began after a driver, application, or update, System Restore or uninstalling that update is less disruptive than resetting Windows.
Use System Restore
- Open Settings > Update & Security > Recovery > Advanced startup > Restart now, or boot WinRE from recovery or installation media.
- Select Troubleshoot > Advanced options > System Restore.
- Choose a restore point dated before the first APC_INDEX_MISMATCH crash. Review the affected programs, confirm the restore, and let Windows restart.
System Restore changes system files, drivers, and registry settings; it does not substitute for a hardware repair and does not normally remove personal documents. If BitLocker is enabled, WinRE may request the recovery key.
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Uninstall a recent quality or feature update
In WinRE choose Troubleshoot > Advanced options > Uninstall Updates, then select the available quality or feature-update option. Use this when the timeline clearly points to an update and no newer compatible driver is available.
Use Startup Repair only for boot failures
Troubleshoot > Advanced options > Startup Repair can correct boot configuration problems, but it is not a general APC driver repair. If Windows starts normally and crashes later, return to the driver, dump, and hardware checks instead.
When should I create USB recovery or installation media?
Use USB media when Windows cannot reach WinRE reliably, the recovery partition is damaged, or you need to repair or reinstall after backing up data. The media gives you access to repair tools; the USB itself does not correct a defective driver or hardware component.
Create Windows 10 installation media
- On a working PC, use Microsoft’s Windows 10 installation-media tool and select the option to create media for another PC.
- Insert a blank USB flash drive with at least 8 GB. The creation process erases the drive, so copy anything important elsewhere first.
- Boot the affected PC from the USB using its one-time boot menu, choose the language and keyboard layout, and select Repair your computer rather than Install now to open WinRE.
Create a Recovery Drive
Search for Recovery Drive, open the wizard, and follow its prompts. The selected USB is erased. A recovery drive can restore a PC even after the internal drive is replaced, but it may not contain the newest device-specific drivers or the manufacturer’s recovery image.
Which fix should I try first?
The least disruptive path is usually the most informative. Use this comparison when deciding whether to keep investigating or move to recovery.
| Remedy | Disruption and data risk | Evidence produced | Reversibility | Compatibility notes |
|---|---|---|---|---|
| Disconnect hardware, Safe Mode, driver rollback | Low; personal files remain | Shows whether a recent device or driver changes the symptom | High; reconnect or reinstall the prior package | Best for graphics, network, storage, USB, audio, and filter drivers |
| Windows, OEM driver, BIOS, and firmware updates | Low to moderate; firmware interruption can be serious | Version comparison and change timeline | Driver updates can usually be rolled back; firmware rollback depends on the vendor | Use exact model and hardware packages |
| Memory Diagnostic | Low; requires a reboot | MemoryDiagnostics-Results event, including Event ID 2001 when no errors are found | Does not alter Windows | A clean result does not clear drivers |
| Dump and WinDbg analysis | Low; requires disk space | Stack, thread state, and candidate modules | Fully reversible | Requires symbols and careful interpretation |
| System Restore or update uninstall | Moderate; removes later drivers, updates, or applications | Restore-point or update timeline | Usually reversible only by another restore or reinstall | Personal files are generally preserved |
| Reset or clean installation | High; applications and settings are removed, and a clean install can erase the system drive | Tests whether the software environment is the cause | Low without a complete backup and installation media | Generic Microsoft media may require separate OEM drivers; OEM recovery media is more device-specific |
| USB recovery or installation media | Low when used for repair; high if used to reinstall | Provides WinRE and installation logs | Repair options are generally reversible; reinstall is not | Blank USB of at least 8 GB is required for installation media, and its contents are erased |
What if APC_INDEX_MISMATCH keeps restarting the PC?
- Photograph the stop screen and disconnect newly added hardware.
- Force WinRE, start Safe Mode, and roll back or uninstall the newest driver or kernel utility.
- Run Windows Update and install exact OEM driver, BIOS, and firmware packages.
- Run
mdschedand inspect the MemoryDiagnostics-Results log. - Enable an automatic memory dump, reproduce the crash once, and inspect it in WinDbg.
- Use System Restore or uninstall the recent update if the timeline supports it.
- Only after backups and driver investigation, consider Reset this PC or a clean installation. If the crash survives a clean, correctly updated installation, suspect RAM, motherboard, storage, firmware, or another hardware defect and arrange hardware service.
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FAQ
Can a blue-screen stop code prove which driver is broken?
No. APC_INDEX_MISMATCH describes the kernel condition, while the named module and dump provide clues. Verify a suspected driver by correlating the timeline, Event Viewer entries, Safe Mode behavior, and repeat crashes after a controlled rollback or update.
Does reinstalling Windows permanently prevent this error?
Only when the underlying cause is damaged software and the replacement installation uses compatible drivers. A failing RAM module, motherboard, storage device, or firmware can produce the same stop code after reinstallation, so hardware testing remains necessary.
Why did the crash start after an antivirus or VPN update?
These products may install kernel filter drivers that intercept file, network, or process operations. Temporarily uninstalling the newest version in Safe Mode, rather than merely disabling its user-interface service, helps determine whether its filter is involved; reinstall only a version confirmed for your Windows build.
What should I do if WinDbg names a Microsoft driver?
A Microsoft filename can be the component that detected corruption, not the component that caused it. Check third-party drivers, RAM, firmware, and recent hardware first, then use the dump stack and reproducible rollback results before removing any system file.
Frequently Asked Questions
Can a blue-screen stop code prove which driver is broken?
No. APC_INDEX_MISMATCH describes the kernel condition, while the named module and dump provide clues. Verify a suspected driver by correlating the timeline, Event Viewer entries, Safe Mode behavior, and repeat crashes after a controlled rollback or update.
Does reinstalling Windows permanently prevent this error?
Only when the underlying cause is damaged software and the replacement installation uses compatible drivers. A failing RAM module, motherboard, storage device, or firmware can produce the same stop code after reinstallation, so hardware testing remains necessary.
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These products may install kernel filter drivers that intercept file, network, or process operations. Temporarily uninstalling the newest version in Safe Mode, rather than merely disabling its user-interface service, helps determine whether its filter is involved; reinstall only a version confirmed for your Windows build.
What should I do if WinDbg names a Microsoft driver?
A Microsoft filename can be the component that detected corruption, not the component that caused it. Check third-party drivers, RAM, firmware, and recent hardware first, then use the dump stack and reproducible rollback results before removing any system file.
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