A four-primary-color organic light emitting display comprising: a display panel where a plurality of first-color pixels, second-color pixels, third-color pixels, and fourth-color pixels are disposed; and a data drive circuit that has a single, digital-to-analog converter to generate first- to fourth-color data voltages and to apply the first-color data voltage to the first-color pixels, the second-color data voltage to the second-color pixels, the third-color data voltage to the third-color pixels, and the fourth-color data voltage to the fourth-color pixels, wherein the maximum grayscale voltages for the first- to fourth-color data voltages are adjusted to be different on a single gamma graph defined as the input grayscale versus output voltage; and a data modulator configured to receive the same number m of bits of first-, second-, third-, and fourth-color digital video data, which is to be displayed in each of the first- to fourth-color pixels, and that is configured to modulate the first- to fourth-color digital video data based on the maximum grayscale values of the first- to fourth-color digital video data individually determined based on luminous efficiency, wherein m is a natural number, wherein, with the first-color pixels having the lowest luminous efficiency and the fourth-color pixels having the highest luminous efficiency, the data modulator is configured to set the maximum grayscale value of the first color at a reference value of 2 m -1, and is configured to bypass first-color digital video data as the modulated first-color video data, and is configured to set the maximum second- and third-color grayscale values to be smaller than the reference value and the maximum fourth-color grayscale value to be smaller than the maximum second- and third-color grayscale values, and is configured to then bypass second-color digital video data as second-color video data if the second-color digital video data does not exceed the second-color maximum grayscale value or to replace second-color digital video data by the second-color maximum grayscale value if second-color digital video data exceeds the second-color maximum grayscale value, and to bypass third-color digital video data as third-color video data if the third-color digital video data does not exceed the third-color maximum grayscale value or to replace third-color digital video data by the third-color maximum grayscale value if third-color digital video data exceeds the third-color maximum grayscale value, and to bypass fourth-color digital video data as fourth-color video data if the fourth-color digital video data does not exceed the fourth-color maximum grayscale value or to replace fourth-color digital video data by the fourth-color maximum grayscale value if fourth-color digital video data exceeds the fourth-color maximum grayscale value. a display panel where a plurality of first-color pixels, second-color pixels, third-color pixels, and fourth-color pixels are disposed; and a data drive circuit that has a single, digital-to-analog converter to generate first- to fourth-color data voltages and to apply the first-color data voltage to the first-color pixels, the second-color data voltage to the second-color pixels, the third-color data voltage to the third-color pixels, and the fourth-color data voltage to the fourth-color pixels, wherein the maximum grayscale voltages for the first- to fourth-color data voltages are adjusted to be different on a single gamma graph defined as the input grayscale versus output voltage; and a data modulator configured to receive the same number m of bits of first-, second-, third-, and fourth-color digital video data, which is to be displayed in each of the first- to fourth-color pixels, and that is configured to modulate the first- to fourth-color digital video data based on the maximum grayscale values of the first- to fourth-color digital video data individually determined based on luminous efficiency, wherein m is a natural number, wherein, with the first-color pixels having the lowest luminous efficiency and the fourth-color pixels having the highest luminous efficiency, the data modulator is configured to set the maximum grayscale value of the first color at a reference value of 2 m -1, and is configured to bypass first-color digital video data as the modulated first-color video data, and is configured to set the maximum second- and third-color grayscale values to be smaller than the reference value and the maximum fourth-color grayscale value to be smaller than the maximum second- and third-color grayscale values, and is configured to then bypass second-color digital video data as second-color video data if the second-color digital video data does not exceed the second-color maximum grayscale value or to replace second-color digital video data by the second-color maximum grayscale value if second-color digital video data exceeds the second-color maximum grayscale value, and to bypass third-color digital video data as third-color video data if the third-color digital video data does not exceed the third-color maximum grayscale value or to replace third-color digital video data by the third-color maximum grayscale value if third-color digital video data exceeds the third-color maximum grayscale value, and to bypass fourth-color digital video data as fourth-color video data if the fourth-color digital video data does not exceed the fourth-color maximum grayscale value or to replace fourth-color digital video data by the fourth-color maximum grayscale value if fourth-color digital video data exceeds the fourth-color maximum grayscale value.