Raghunathan In conventional 8051's the hardware will respond just like the clock conditioner circuitry no known reason for failure. the memory may be different and I suspect variant dependent. I just read an article in one of the system design publications on the newer 65 nanometer technology used in high speed dsp's and processors. The conclusion is that at these levels electro migration will cause failure in 3 to seven years. this may show up in the ultra high speed variants Terry