At the heart of a modern digital telephone exchange is the processor system designed to control it. This must be reliable, flexible and have high performance. A modular distributed processor architecture has been designed which meets these requirements. This is made up of a number of loosely coupled processor modules linked by a highly reliable braided-ring communications system. The operating system is distributed over the modules in the system. Recovery algorithms are built in so that the system will continue to operate if any part of it fails.