Abstract: A system for controlling access such as time access by a user to a store of information in an information storage system which uses unique codes associated with corresponding number of information units. The system includes a key storage unit (18) which is specifically formatted and can only be accessed by a special read/write program available to the distributor or manufacturer. The key storage unit (18) has a plurality of keys (16) which act as addresses for time units which control the time of operation the program is to be run using the host system clock (14). In response to a valid key being given to the user and being entered to start the program, the number of timed units for this code is rendered subsequently inaccessible, by for example being set to zero automatically so that it cannot readily be used again for free. The program can then be run continuously until an accumulated predetermined time is reached and at the end of the time, program operation is terminated.