A cooling system for a computer system, said computer system comprising - at least one unit such as a central processing unit venerating thermal energy and said cooling system intended for cooling the at least one processing unit and the cooling system comprising - a liquid reservoir housing comprising an inlet tube connection and an outlet tube connection both attached to the reservoir housing, - a heat radiator connected by means of connecting tubes (24, 25) to the inlet tube connection and the outlet tube connection of the reservoir hosing, - a liquid reservoir provided in the reservoir housing, said liquid reservoir having an amount of cooling liquid, said cooling liquid intended for accumulating and transferring of thermal energy dissipated from the processing unit to the cooling liquid, wherein the reservoir is further provided with channels for establishing a certain flow-path for the cooling liquid, - a pump being provided inside said reservoir housing as part of an integrate element, said pump comprising an impeller which is positioned in a separate recess of the channels, where the recess has a size corresponding to the diameter of the impeller of the pump, and has a recess inlet and a recess outlet which is connected to the outlet tube connection, - a heat exchanger comprising a heat exchanging interface for providing thermal contact between the processing unit and the cooling liquid for dissipating heat from the processing unit to the cooling liquid, where the heat exchanging interface comprises a heat exchanging surface that constitutes part of the liquid reservoir housing facing the processing unit, where the channels face an inner surface of the heat exchanging interface forcing the cooling liquid to pass the heat exchanging surface, said integrate element comprising the heat exchanging interface, the reservoir housing and the pump, wherein - said pump is intended for pumping the cooling liquid from the heat radiator into the reservoir housing through the tube inlet connection, through the channels, into the pump through the recess inlet and from the pump through the recess outlet, through the channels and the tube outlet connection to the heat radiator, - said heat radiator intended for radiating thermal energy from the cooling liquid, dissipated to the cooling liquid, to surroundings of the heat radiator. - at least one unit such as a central processing unit venerating thermal energy and said cooling system intended for cooling the at least one processing unit and the cooling system comprising - a liquid reservoir housing comprising an inlet tube connection and an outlet tube connection both attached to the reservoir housing, - a heat radiator connected by means of connecting tubes (24, 25) to the inlet tube connection and the outlet tube connection of the reservoir hosing, - a liquid reservoir provided in the reservoir housing, said liquid reservoir having an amount of cooling liquid, said cooling liquid intended for accumulating and transferring of thermal energy dissipated from the processing unit to the cooling liquid, wherein the reservoir is further provided with channels for establishing a certain flow-path for the cooling liquid, - a pump being provided inside said reservoir housing as part of an integrate element, said pump comprising an impeller which is positioned in a separate recess of the channels, where the recess has a size corresponding to the diameter of the impeller of the pump, and has a recess inlet and a recess outlet which is connected to the outlet tube connection, - a heat exchanger comprising a heat exchanging interface for providing thermal contact between the processing unit and the cooling liquid for dissipating heat from the processing unit to the cooling liquid, where the heat exchanging interface comprises a heat exchanging surface that constitutes part of the liquid reservoir housing facing the processing unit, - said pump is intended for pumping the cooling liquid from the heat radiator into the reservoir housing through the tube inlet connection, through the channels, into the pump through the recess inlet and from the pump through the recess outlet, through the channels and the tube outlet connection to the heat radiator, - said heat radiator intended for radiating thermal energy from the cooling liquid, dissipated to the cooling liquid, to surroundings of the heat radiator.