Saint F00F, Church Father Who Froze the Pentium

Patron of Pentium processors, illegal instructions, and whoever discovered that four bytes could stop everything.

Life

In November 1997 word spread that a malformed Pentium instruction, a locked CMPXCHG8B that began with the bytes F0 0F C7 C8, sent the processor into a complete halt: the system froze and needed a reboot. Any unprivileged program could run it, on Windows as on Unix. There was no microcode to update: the operating systems had to learn to intercept the instruction before it did harm.

Prayer

O Saint F00F, who stops the heart of the machine with four bytes, let our systems survive the sick instructions. Amen.

How to celebrate

Celebrated by updating the operating system with the interrupt-table fix (the "F00F workaround").

Four bytes are enough to silence a giant.