INFORMATION PROCESSOR

PURPOSE:To eliminate a physical restriction in the mounting of an I/O device by automatically setting the allocation of a writing buffer exclusively used for the I/O device by depending on presence or absence of an input/output device at the time of starting a system. CONSTITUTION:A memory 1 is connected to a memory bus 8, the I/O devices 4-6 are connected to an I/O bus 7 and the memory bus 8 and the I/O bus 7 are connected with bus connecting mechanism 2. I/O control mechanism 3 is connected to the I/O bus 7. Bus connecting mechanism 2 has a writing buffer 2-2 which is exclusively used in the respective I/O devices by memory writing from the respective I/O devices and I/O control mechanism 3 has an allocation table 3-1 which recognizes presence or absence of mounting of the I/O device at the time of starting the system and presence or absence of buffer usage, allocates the writing buffer and holds it. The respective I/O devices have a channel holding part holding allocation channel information reported from I/O control mechanism 3.