Long term failure rates are not usually measured in realtime but in deliberately heat elevated environments which simulate many years of stresses in a few months. This work is essential to ensure design decisions they've made don't accidentally cause their chips to fail after 2 years (which might be outside warranty lifetime but would still result in class action law suits and horrible publicity).
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It doesn't seem worth it for Intel to measure MTBF. By the time they got good numbers for a specific chip, they'd be trying to sell its successor.
Long term failure rates are not usually measured in realtime but in deliberately heat elevated environments which simulate many years of stresses in a few months. This work is essential to ensure design decisions they've made don't accidentally cause their chips to fail after 2 years (which might be outside warranty lifetime but would still result in class action law suits and horrible publicity).
Intel guarantees their consumer CPUs for 3 years.
http://www.intel.com/support/processors/sb/cs-020033.htm