A study has been made of the performance of the PRIME computer system at Canterbury University. The PRIME is essentially an interactive system. The performance parameter of most interest to users sitting at a terminal is response time, defined by Abrams as, "the elapsed time from the last user keystroke until the first meaningful character is displayed at the user's terminal". A system's responsiveness is degraded, resource bottlenecks. Thus a major aim look for possible bottlenecks which effect on response time performance. An initial general study showed: often quite seriously, by of the study has been to might be having such an (1) the shortcomings of software monitoring, (2) that disk IO seemed to be a problem. It was therefore decided to build a disk monitor to concentrate monitoring on this area of system performance. Limitations were encountered using this monitor and from the experience gained in monitoring the disk, the specifications for an ideal disk monitoring tool were developed.