Orders for the machine are presented to it in coded form on punched tape, and are translated by the machine itself into the form in which they are held in the store, in accordance with a standard set of 'initial orders'. In the course of this input of orders it is possible to use the machine to make systematic modifications to the orders as punched on the tape; the modifications required, if any, are indicated by a code letter included in each order as punched on the tape. This system allows the use of a more flexible system of representing orders than the binary form used inside the machine. It also enables sub-routines to be drawn up in a form independent of the particular values of parameters in them, the values of these parameters in any particular application of the sub-routine being inserted by the machine in the course of the initial input of orders, or in the course of operation of the machine. This simplifies the formation of a library of sub-routines and its use in the construction of long programmes. A complete example is worked.