With the use of giant magneto-resistive (GMR) head, thermal asperity (TA) has been a big concern in drive industry. In this study, we investigated several heads and disk related factors that affect the TA sensitivity of the drive. TA experiments were conducted by introducing the particles in the drives using a particle injection chamber. It is found that the slider ABS shape can help to reduce TA or contamination at the head/media interface. However, TA sensitivity of the drive mainly depended on the intrinsic property of GMR sensor. TA sensitivity of head increases as the bias current increases. GMR head is much less sensitive to TA compared with MR head. However, if similar bias current is applied to both MR and GMR heads, TA sensitivity of GMR head became almost identical to that of MR head. TA sensitivity of different types of disks was also studied and the dominant factor affecting the TA sensitivity is observed to be the scratch resistance of the carbon overcoat layer.