A computer system includes an enclosure having an air intake, a heat sink and an electronic element. The heat sink includes a first heat dissipating portion, a second heat dissipating portion, and a third heat dissipating portion interconnecting the first and second heat dissipating portions. Each of the first heat dissipating portion, second heat dissipating portion, and third heat dissipating portion includes a number of fins and passages formed between each two adjacent fins. The passages of the first heat dissipating portion face toward the air intake. A space is maintained between the first heat dissipating portion and the second heat dissipating portion, and the electronic element is mounted in the space.