In an attempt to decrease the amount of labour involved between diffraction data and structure analysis and to increase the flexibility of large scale operation, we have developed an organizational system for the use of large computers for crystallographic problems. This system has two main new features. The first is a convention for storing all types of data and computational results in serial lists. The second is that operational control is organized by a master programme which moves data (individual items, lists and programmes) from one storage medium to another and enters programmes. All programmes assume that the data necessary are available in the main store, and consequently are written using the list convention without further input or output facilities. Operations on lists are performed serially by programmes entered from the master programme which reads the user's set of consecutive instructions. A symbolic language compiler is available as part of the system to compile users' own programmes.