a heat dissipating device includes a heat sink , a heat pipe , a heat reservoir thermally connecting with the heat sink through the heat pipe , and a fan generating an airflow through the heat sink . the heat pipe includes an evaporating portion attached to the heat sink and a condensing portion attached to the heat reservoir . the heat reservoir is made of metal containing working medium , such as water , therein . the heat reservoir stores or releases heat based on the amount of heat generated by the cpu to realize a compensation to the increase or decrease of temperature of the cpu , whereby the change rate of the temperature of the cpu from idle to busy condition and vice versa can be more stable .