Extreme black hole entropy obtained in an operational approach

The entropy of anti-de Sitter Reissner-Nordstrom black hole is found to be stored in the material which gathers to form it and equals to A/4 regardles s of material states. Extending the study to two kinds of extreme black hol es, we find different entropy results for the first kind of extreme black h ole due to different material states. However for the second kind of extrem e black hole the results of entropy are uniform independently of the materi al states. Relations between these results and the stability of two kinds o f extreme black holes have been addressed.