Updating display screens of local and remote workstations

Two computer workstations are connected together by a communications link 300. One workstation (the local workstation) 100 includes a window which is used to display a copy of what is currently being displayed on the screen of the other (remote) workstation 200. Each time an update is made to the screen of the remote workstation, it must be transmitted to the local workstation. A bounding rectangle for the area of the screen clanged by the update is determined. If the bounding rectangle is greater than a predetermined size, then a first packet is transmitted from the remote workstation to the local workstation, prior to the transmission of the actual update data itself. This first packet indicates the bounding rectangle. The local workstation responds to the first packet by greying (shading) the corresponding region of the window which contains the copy of the remote screen, thereby indicating to a user of the local screen that an update is imminent.