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For the first time, damage thresholds for TMR and GMR read sensors were measured using pulses with widths ranging from 40 ps to 2.3 ns. The ultra-fast pulses were generated using a novel Ultra-Fast Transmission Line Pulsing (UFTLP) system. The damage voltage level for the TMR and GMR heads was about 0.6 V using 2.3 ns-wide pulses, and increased to about 2.0 V using 40 ps-wide pulses. However, the damage current level for the TMR design was about 4 mA, about an order of magnitude lower than the GMR design. It is important to measure the failure level using pulses with pulse widths less than 1 ns wide because write-to-read crosstalk can produce such transients during writing. It is concluded that damage to the reader from 500 ps-wide write-to-read crosstalk transients will occur if it exceeds approximately 1 V.