The 1980s saw big steps in signalling technology as relay based systems began to be superseded by microprocessor based equipment. These interlockings and control centres are now more than 20 years old and the hardware and software components that they use have been rendered obsolete by rapid advances of computing and communications technology. This in itself is not a problem for the railway, as the systems are generally reliable and continue to deliver their operational and safety requirements, but it becomes an issue when there is a need to replace failed components or make changes to respond to new traffic demands. The problem is not unique to this particular generation of equipment: it also applies to older systems using analogue electronics and newer software based systems.