Error 0xc000001d, "An illegal instruction was executed"

This code is Windows saying a program tried to run a CPU instruction that the processor does not support or cannot execute. Microsoft's name for it is STATUS_ILLEGAL_INSTRUCTION. It happens most when a program was built for a newer processor than the one in the PC, when a file is damaged, or when an unstable overclock corrupts the data being run.

The fix, in order

  1. Check the program's minimum requirements. Look up your processor model and compare it with the requirements the maker lists. Some modern games and apps need instruction sets like AVX2 that older processors lack, and no setting can add them.
  2. Update the program. The maker may have fixed a bad build or added a version for older processors. Install the latest update from the official source, or check whether the maker offers a legacy build.
  3. Reset any overclock to stock speeds. If the CPU or RAM is overclocked, restore default settings in the BIOS or the tuning software and test again. An unstable overclock is a common cause of this exact error.
  4. Reinstall the program. A damaged download or a corrupted file can make the CPU read garbage as instructions. Uninstall, restart, and install a fresh download from the official source.
  5. Test the RAM. Search for Windows Memory Diagnostic, run it, and restart when asked. Faulty RAM can corrupt program code as it loads, which surfaces as an illegal instruction.
  6. Update the BIOS and chipset drivers from the PC or motherboard maker's support page. A BIOS update can add proper support for newer instruction sets on a processor that already has them.
  7. Repair Windows files. In an admin Command Prompt run sfc /scannow, then DISM /Online /Cleanup-Image /RestoreHealth.
If your processor is too old for the program, there is no software workaround. Compatibility modes and DLL tricks cannot give a CPU an instruction set it lacks. The honest options are an older version of the program, a different program, or a processor upgrade.

If it still happens

If the error appears in many different programs, suspect the hardware, so test the RAM, reset the BIOS to defaults, and check temperatures, since overheating can also corrupt execution. If it appears in only one program on a processor that meets the requirements, the program's own files are the likeliest cause, so try a clean reinstall and report the crash to the maker with your processor model included.

Common questions

Does 0xc000001d mean my CPU is broken? Usually not. The most common cause is a program built for a newer processor running on an older one, or a damaged program file. A genuinely faulty CPU is possible but rare, and it would usually cause crashes in many programs, not just one.

Why does 0xc000001d happen only in one game? Games are often built with newer CPU instructions for speed, and one game may use an instruction set your processor lacks while other games do not. Check the game's minimum system requirements against your processor, and look for an update or a compatibility option from the maker.

Can overclocking cause 0xc000001d? Yes. An unstable overclock can corrupt the data a program reads, so the CPU ends up trying to run bytes that are not valid instructions. Resetting the CPU and RAM to stock speeds is a quick test, and if the error goes away, the overclock was the cause.

Related errors

Error 0xc0000005 · Error 0xc0000409 · Error 0xc000007b

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