A computer-implemented method performed within a portal server system is disclosed. In one embodiment, the system may comprise a graphics processor, a frame buffer, a sample cache, and a sample-to-pixel calculation unit. By this foldback circuit, an issue of directivity of the radio signals can be reduced, an effective read range of the radio signals can be increased, as well as a near field induction function and a far field induction function can be provided at a same time. The memory map specifies, for each page, a number of memory cells for storing data, and a number of memory cells for storing overhead. An air discharge port is formed at the bottom of the annular groove.