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The Pentium F00F bug is a design flaw in the majority of Intel Pentium, Pentium MMX, and Pentium OverDrive processors (all in the P5 microarchitecture). Discovered in 1997, it can result in the processor ceasing to function until the computer is physically rebooted. The bug has been circumvented through operating system updates.
The name is shorthand for F0 0F C7 C8, the hexadecimal encoding of one offending instruction. More formally, the bug is called the invalid operand with locked CMPXCHG8B instruction bug.

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