Organic light emitting diode display device including compensating unit and method driving the same

An organic light emitting diode (OLED) display device comprises a driving transistor Td, first and fourth transistors T1, T4 connected to the driving transistor, a second transistor T2 connected between a data voltage Vdata and the driving transistor, a third transistor T3 between a high level voltage Vdd and the driving transistor, a fifth transistor T5 between an initial voltage Vini and the driving transistor, a sixth transistor T6 connected to the initial voltage, a seventh transistor T7 connected to the high level voltage, an eighth transistor T8 connected to a reference voltage Vref, a storage capacitor Cst between the driving transistor and the eighth transistor, and a light emitting diode between a low level voltage Vss and the fourth transistor. Driving an OLED display comprising 8 transistors and a capacitor comprises four time periods. The first period supplies an initial voltage and a reference voltage to first and second electrodes respectively of the capacitor. The second period supplies a data voltage to the first electrode. The fourth period supplies a high level voltage to the second electrode of the storage capacitor and a driving transistor.