An image forming apparatus capable of realizing miniaturization of apparatus and low cost is supplied. Only one enabled operating system at a time has control of hardware resources of the computing device. It is preferable to adjust the concentration of the doped impurity in such a manner that a collector-base depletion layer extends up to the first collector layer. The transport overhead area includes transport supervision data related and an area of fixed patterns. The plurality of turbo decoders is arranged in parallel, and the system is further provided with an allocating device coupled between the system input and the turbo decoder inputs for dynamically allocating the turbo coded bits to one of the turbo decoders.