UNEXPECTED_KERNEL_MODE_TRAP Blue Screen 0x7F: Five Trap Numbers Microsoft Names

UNEXPECTED_KERNEL_MODE_TRAP is Windows stop code 0x0000007F (0x7F). Microsoft's reference says it "indicates that the Intel CPU generated a trap and the kernel failed to catch this trap." The trap is either a bound trap, which the kernel isn't permitted to catch, or a double fault, which always results in a system failure.

Unusually, Microsoft's page includes a full Troubleshoot section with separate hardware and software lists, so it gives more to non-programmers than most stop codes.

This page is built from the Microsoft Learn article "Bug Check 0x7F: UNEXPECTED_KERNEL_MODE_TRAP" and, where noted, Microsoft's general page on analysing blue screen data, both read on 13 October 2026 and checked against the Microsoft Docs source files. Microsoft marks the 0x7F page as written for programmers and directs customers to https://www.windows.com/stopcode. Anything taken from the general page rather than the 0x7F page is labelled as such.

What does the first parameter say?

The first parameter that appears on the blue screen is the trap number. Microsoft lists the most common ones:

Trap number	Trap name	What Microsoft says it indicates
0x00000000	Divide by Zero Error	A DIV instruction is executed and the divisor is zero; memory corruption, other hardware problems or software failures can cause it
0x00000004	Overflow	The processor executes a call to an interrupt handler when the overflow (OF) flag is set
0x00000005	Bounds Check Fault	The processor, while executing a BOUND instruction, finds that the operand exceeds the specified limits
0x00000006	Invalid Opcode	The processor tries to execute an invalid instruction; typically the instruction pointer has become corrupted, and the most common cause is hardware memory corruption
0x00000008	Double Fault	An exception occurs during a call to the handler for a prior exception

The other three parameters are not described on the page. Microsoft lists less common trap numbers too, such as 0x00000003 (a debugger breakpoint), 0x0000000D (GP_FAULT, a protection fault pertaining to access violations) and 0x00000011 (an alignment check exception), and refers readers to the Intel processor architecture manual for numbers not listed.

What causes a double fault?

The double fault, trap number 8, is the one Microsoft explains at length. A double fault means an exception happened while the processor was already handling an earlier one. Microsoft names two common causes:

• A kernel stack overflow. This happens when a guard page is hit and the kernel tries to push a trap frame. Because there is no stack left, a stack overflow results, causing the double fault.
• A hardware problem.

For the overflow case, Microsoft says a developer can use the !thread extension to find the stack limits and the kb command with a large value, for example kb 100, to display the full stack. In the Cause section it adds that a stack overflow can happen "if multiple drivers are attached to the same stack," with the example of two file system filter drivers attached to the same stack where the file system recurses back in.

What does Microsoft say about hardware?

The Troubleshoot section starts with hardware, which is unusual for a driver-oriented bug check.

Hardware check	What Microsoft says
Recently added hardware	Remove it to see if the error recurs
Failed existing hardware	Remove or replace the faulty component and run the hardware diagnostics the system manufacturer supplies
Memory	Faulty or mismatched memory can cause this bug check; use the memory diagnostic program in Windows to test all of the system memory
Disk drives and controllers	Confirm that all hard disk drives and controllers are compatible with the installed version of Windows
Motherboard and power supply	A scratched trace or defective component on the motherboard can cause issues, and a failing power supply can too
Overclocking	Setting the CPU above its rated speed can cause this error; return the CPU to the default clock speed, and disable memory caching of the BIOS if that option is available

Microsoft says the bug check "typically occurs after you install faulty or mismatched hardware, especially memory, or if installed hardware fails."

What does Microsoft say about software?

The software list covers the System Log in Event Viewer, availability of updates for the ACPI/BIOS, the hard-drive controller or network cards, and what to do after a new or updated driver: remove or replace it, using Safe Mode to rename or delete the faulty driver if the error occurs during startup, or the Recovery Console if the driver is used by Safe Mode itself. It also mentions the Last Known Good Configuration option, which Microsoft says is most effective when you add only one driver or service at a time.

If the error appears while upgrading to a new version of Windows, Microsoft says incompatible software may be to blame: a device driver, a system service, a virus scanner or a backup tool. The advice is to remove all third-party device drivers and system services, disable virus scanners before upgrading, contact the maker for updates, and install the latest Windows updates.

What Microsoft tells non-programmers to do

Microsoft's Troubleshoot section for 0x7F can be followed without a debugger. In order, the hardware list comes first and then the software list:

• Remove recently added hardware; replace any failed hardware and run the manufacturer's diagnostics.
• Test all system memory with the memory diagnostic program in Windows.
• Confirm disk drives and controllers are compatible with your Windows version.
• If you overclocked the CPU, return it to the default clock speed.
• Check the System Log and look for ACPI/BIOS, controller and network card updates.
• After a new or updated driver, remove or replace it, using Safe Mode if the error happens at startup.

This is the longest customer-facing list of any stop code on this site. It still does not promise a fix.

Checklist before changing anything

• Trap number (parameter 1) from the System Log
• Hardware or memory added or changed recently
• Whether the CPU or memory is overclocked
• Results of the Windows memory diagnostic
• Drivers installed or updated just before the first crash

How to work through a 0x7F blue screen

• Note the trap number from the blue screen or System Log
• Remove recent hardware and test the memory
• Undo any overclocking
• Remove or roll back a recent driver, then check for firmware updates

Registry edits and paid tools. Microsoft's page does not mention them, so neither does this one.

What does Microsoft's Debug section say to run?

The 0x7F page has its own Debug section, and it is explicit about the order. Always begin with the !analyze extension using the -v (verbose) option, examine the output and the faulting code, and look for recurring trends across multiple dumps. After !analyze, use the kv stack backtrace command. What comes next depends on what kv shows: if it shows a task gate, use the .tss command on the part before the colon; if it shows a trap frame, use .trap to format the frame. The branch matters because a task gate and a trap frame are two different records of the same crash.

Every stop code covered here is listed in our Windows blue screen stop code index.

Sources and how to check

• Microsoft Learn, "Bug Check 0x7F: UNEXPECTED_KERNEL_MODE_TRAP" — https://learn.microsoft.com/en-us/windows-hardware/drivers/debugger/bug-check-0x7f--unexpected-kernel-mode-trap. Source file in the MicrosoftDocs/windows-driver-docs repository.
• Microsoft Learn, "Analyze bug check (stop code error) data" — https://learn.microsoft.com/en-us/windows-hardware/drivers/debugger/blue-screen-data (general guide).
• Bug check code reference, Microsoft Learn: https://learn.microsoft.com/en-us/windows-hardware/drivers/debugger/bug-check-code-reference2
• Troubleshoot blue screen errors (for regular users): https://www.windows.com/stopcode
• Licence and credit: Microsoft Learn documentation is published under CC BY 4.0. This page selects, rewords and reorders it, adds a plain-language reading, and is not endorsed by Microsoft. The original is linked above.
• Checked as of 13 October 2026.