Abstract: In a computer system (1) having only six positions for representing dates, information on which century that is referred to is contained in one or several of the six positions without changing the date format, a so called Roman format. In a preferred embodiment the information on that a particular date refers to a date in the twenty-first century instead of a date in the twentieth century is included by means of letting the months of the twenty-first century be represented by the numbers 21-32 in contrast to the months of the twentieth century which are represented by the numbers 1-12. This date format, the Roman format, solves a number of problems encountered by the so called millennium problem. Thus, less reprogramming of existing computer systems will need to be performed when using this representation.