Abstract: A method and apparatus for identifying the failing equipment in a computer system when a failure condition is experienced by a computer operator while accessing a computer input/output channel. The apparatus has a memory system which records pre- and post-failure events, which recordings are used for analyzing signal activity on the input/output channel. The signals retained in memory may be output to a hard copy device in an easily understood format to provide a picture or input/output bus activity for the time surrounding the failure event. The operator may utilize the hard copy output to rapidly diagnose the cause of computer failure.