PURPOSE: To carry out a disconnection mode with high efficiency by checking the contents of a disconnection queue to secure the disconnection mode when a bus is controlled in response to a new start request.
CONSTITUTION: An adaptor 4 receives the start of a command given to a certain input/output device and checks whether said input/output device belongs to a group A or B. When the input/output device belongs to the group A, it is checked based on the contents of a disconnection queue 14B, whether some input/output device to which the bus control is opened in a disconnection mode exists or not among those input/output devices 6Bi of the group B connected to an input/output bus 5B. Then an input/output device of the group A is started in the disconnection mode when the contents of the queue 14B are idle. While an input/output device of the group A is started in a connection mode when the contents of the queue 14B are not idle. In such a way, the operations are carried out with high efficiency in the disconnection mode.
YOSHIYA YUKIHIRO
KATAYAMA KAZUTOSHI
