Abstract: A computer network (FIG. 1) comprises a plurality of personal computers (PCs 10), groups of which are each logically connected to a different one of a plurality of intermediate computers (11). At least one of the intermediate computers is connected to a mainframe computer (12). File and resource serving and locking services are provided transparently to PC user programs (200). Certain user service requests ("open file" and "exit" calls) on each PC to the PC operating systems means (20,22) are trapped by an operating system kernel-level patch (21), and corresponding requests are sent to a kernel-level driver (31) on the associated intermediate computer. The driver collects requests from all PCs associated with the intermediate computer and funnels them to a user level request server (32) on the intermediate computer.