Red Hat Knowledgebase

A Machine Check Exception (MCE) is an operating system error which occurs when a computer processor detects an unrecoverable hardware problem.

The error is usually due to failure or overstressing of hardware components where the error cannot be more specifically identified with another error message. Diagnosing the error message can be difficult, although Intel Pentium processors do generate more specific codes which can be decoded by contacting the manufacturer.

MCEs require a restart to continue and often indicate a long term general problem.

Here are some of the main hardware problems that cause MCEs:

• System bus errors (error communicating between the processor and the motherboard)
• Memory errors that may include parity / Error correction code (ECC) problems. Error checking ensures that data is stored correctly in the RAM, if information is corrupted then random errors occur.
• Cache errors in the processor, the cache stores important data and code. If this is corrupted errors often occur

Normal causes for MCE errors are overheating and incorrect hardware installation. Overheating can cause electrons to become more animated and so escape from the silicon tracks corrupting data. Some specific manual causes could be:

• Overclocking (naturally increases heat output)
• Poorly fitted heatsink/fans

Computer software can also cause errors in this way (normally by corrupting data they are reading or writing). For example:

• Software performing read/writes to non-existent memory regions confuses the processor / system bus.
• Certain sequences of operations may trigger processors to become confused - for example if too many programs are used at the same time.