Abstract: Disclosed herein is a network hard disk copy system for managing multiple clients. The system includes a main PC and sub PCs. The main PC generates a check parity signal, transmits it to sub PCs, receives response messages from the sub PCs, checks arrival times of the response messages, determines sub PCs which sent the response messages within a reference time to be those of a first group, copies data to the sub PCs of the first group, divides sub PCs which could not send the response messages within the reference time into groups, classifies sub PCs having faster response message arrival times as sub PCs of a higher group, generates and transmits global group information to sub PCs, and transmits group information output signals. The sub PCs extract their own group information from the global group information, and generate and output background images including the group information.