The invention relates to a computer system (50) comprising at least one central processing unit (1) and at least one data bus (30) that is connected to the central processing unit and memory elements (4,20,60,70), which comprise at least one programme memory (15, 20) and one or more test data memories (16, 60, 70). The test data memory constitutes part (16, 60) of the programme memory (4, 20) and/or part (70) of a separately located memory element. At least one test data generation device (3, 6, 8, 90, 100) is provided for evaluating and/or saving data (80) that is present in the data bus and/or for generating test data (130, 140, 160). The invention also relates to a method for identifying errors when the programme memory (4, 20) is being accessed. According to said method, test data, which has been generated using the data to be saved, is additionally stored in columns and an error identification device (3, 6, 8, 90, 100) independently accesses the data bus (30) and/or the address bus (21), and/or the error identification device tracks the bus traffic initiated by the central processing unit (1) and collects data.