The present invention relates to a screw compressor and a method for operating the compressor primarily for gaseous refrigerants, comprising a compressor housing (4) and a male (8) and a female (10) screw rotor arranged in screw rotor bores in the compressor housing (4), which male and female rotor are co-rotatingly drivable and interacting for compressing the refrigerant, which screw compressor comprises at least one slider (22) movable in relation to the male and the female rotor, where movement of the slider controls the internal volume ratio of the screw compressor, which slider is moveable in a slider housing (20) in a direction sideways to the plane formed by the rotational axes of the male and the female rotor, which slider, interacting with the male and the female rotor, comprises at least two surfaces (152, 154) cooperating with subsequent surfaces (156, 158) placed in conjunction with the slider housing for controlling the angular and linear placement of the slider in its forward position.