Abstract: A computer comprises a write monitor unit for monitoring a data write operation into an operating system file, an update data file for storing update data upon detection of a data write operation, an update-log file for storing the history information for the update data in the case where the update data is stored, and a read monitor unit for reading data from the update data file in the case where the history information for the data to be read from the operating system file is stored and reading data from the operating system file in the case where the history information is not stored.

Abstract: Even when a client unit 2 can not connect with a server unit 1, by comparing a system information held by a system information file 23 with the present status, a self-diagnosis is performed by a self-maintenance system file 24 of the client unit 2 itself, and as a result, when abnormality has occurred, the client unit 2 independently carries out recovering processing in accordance with its own backup file 25. When it is possible to connect with the server unit 1, the necessary information is obtained from the server unit 1 to carry out recovering processing and system update processing. By this processing, the following problem is settled: In case of an obstacle to the client in the conventional client/server system which is based on the premise of it being normally connectable with the server, when it becomes impossible to connect to a server, the client is prevented from downloading from the server the files necessary for maintenance processing.

Abstract: Each client unit 2 diagnoses its operation environment (hardware, software, firmware and so on) at the start time of itself, and when an abnormality or any change (deletion, modification or creation) has occurred and it is repairable, the client unit 2 itself repairs itself or maintenance process is conducted by reinstallation from the server unit 1. When it is unrepairable, the client unit 2 releases itself from the LAN line 100. In this way, by having the client unit 2 be provided with self maintenance capability to allow each client unit 2 to conduct the self maintenance of itself such a client/server system is realized by which loads of the server unit 1 and the LAN line 100 are reduced as well as the probability of system down occurrence is lowered, further the capability of the entire system is improved and a maintenance engineer or a user is not required much labor.