A computer includes an enclosure, and a mainframe module enclosed in the enclosure. The mainframe module includes a base board defining a motherboard, a plurality of drive devices, a heat sink device and a fan thereon. The heat sink device includes a heat sink having a plurality of fins and a heat pipe. The base board is divided into a first part and a second part. The motherboard is located in the first part, and the drive devices are located in the second part. The fan is located between the first and second parts. The heat pipe transmits heat from a heat source on the motherboard to the plurality of fins. The fan blows air to the plurality of fins to cool the heat source on the motherboard.