Windows 7 / Getting Started

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Stop 0x7F or UNEXPECTED_KERNEL_MODE_TRAP

The Stop 0x7F message indicates that one of three types of problems occurred in kernel mode:

• A condition that the kernel is not allowed to have or intercept (also known as a bound trap)
• Software problems
• Hardware failures

Interpreting the Message

This Stop message has four parameters:

1. Processor exception code.
2. This value is 0x00 (zero).
3. This value is 0x00 (zero).
4. This value is 0x00 (zero).

The first parameter is the most important and can have several different values, indicating different causes of this error. You can find all conditions that cause a Stop 0x7F in any x86 microprocessor reference manual because they are specific to the x86 platform. Some of the most common exception codes are the following:

• 0x00, or a divide-by-zero error, occurs when a divide (DIV) instruction is run and the divisor is 0. Memory corruption, other hardware failures, or software problems can cause this message.
• 0x04, or Overflow, occurs when the processor carries out a call to an interrupt handler when the overflow (OF) flag is set.
• 0x05, or Bounds Check Fault, indicates that the processor, while carrying out a BOUND instruction, found that the operand exceeded the specified limits. BOUND instructions are used to ensure that a signed array index is within a certain range.
• 0x06, or Invalid Opcode, is generated when the processor attempts to run an invalid instruction. This typically occurs when the instruction pointer is corrupted as a result of a hardware memory problem and is pointing to a wrong location.
• 0x08, or Double Fault, indicates an exception while trying to call the handler for a prior exception. Normally, two exceptions can be handled serially, but certain exceptions (almost always caused by hardware problems) cause the processor to signal a double fault.

Less common codes include the following:

• 0x01 A system-debugger call
• 0x03 A debugger breakpoint
• 0x0A A corrupted Task State Segment
• 0x0B An access to a memory segment that was not present
• 0x0C An access to memory beyond the limits of a stack
• 0x0D An exception not covered by some other exception; a protection fault that pertains to access violations for applications

Resolving the Problem

The following suggestions are specific to Stop 0x7F errors. For additional troubleshooting suggestions that apply to all Stop errors, see the section titled "Stop Message Checklist" later in this tutorial.

• Stop 0x7F messages are typically the result of defective, malfunctioning, or failed memory hardware. If you added new hardware recently, remove and replace the hardware to determine whether it is causing or contributing to the problem. Run Windows Memory Diagnostics to determine whether the feature has failed.
• Running the CPU beyond the rated specification, known as overclocking, can cause Stop 0x7F or other error messages because of heat buildup. When diagnosing problems on overclocked systems, first restore all clock and bus speed settings to the manufacturer-recommended values to determine whether this resolves the issues.
• The problem might also be due to cracks, scratched traces, or defective features on the motherboard. If all else fails, take the system motherboard to a repair facility for diagnostic testing.
• Stop 0x7F messages can occur after you install incompatible applications, drivers, or system services. Contact the software manufacturer about possible Windows 7-specific updates. Using updated software is especially important for backup programs, multimedia applications, antivirus scanners, and CD mastering tools.

More Info For more information about Stop 0x7F messages, see the Knowledge Base at http://support.microsoft.com/. Search the Knowledge Base using the keywords 0x0000007F and 0x7F.