Abstract: A data transmission method is provided which transfers data to an adapter from a processor module and transfers the data to an input/output device from the adapter. The method includes the following steps. The first step is to transfer data from the processor module to a data buffer provided in the adapter. The data buffer has a storage capacity equal to or greater than a predetermined storage capacity. The second step is to determine whether or not an error occurs in the processor module during the first step. The third step is to determine whether or not the data has been completely transferred to the data buffer provided in the adapter without having any error. The fourth step is to transfer the data in the data buffer provided in the adapter to the input/output device when the third step determines that the data has been completely transferred without error to the data buffer provided in the adapter.