A testing method of bending stress and a testing apparatus thereof are provided. The transfer module retrieves a first transfer list including an address of a first storage area, which is set on the first memory for a read command, from the server module. A transcoder coupled to the controller may be configured to convert the cached version of the requested video stream to a lower video definition format if the video definition format of the cached version is determined to be higher than the video definition format of the requested video stream. After processing the received service requests, the computer system returns to the lowest power state. The stepped profile is designed such that the heights of the steps of a pattern element introduce phase changes that equal at least two different multiples of 2\u03c0 for one of the three wavelengths and equal at least two different phase changes modulo 2\u03c0 for one of the two other wavelengths.