Abstract: Disclosed is an error-tracking unit within a data processing system. Each data location to be checked for error and to be located in the case of an error is provided with error detection circuitry. Each data location is additionally provided with an error history register for storing an error signal. When the error-detecting circuit detects an error, the error history register is enabled to store the error signal. Whenever an error is detected, the error history registers are inhibited from further change so that errors are not propagated. The error detection also causes a machine check signal which, in general, prevents the data processing system from normal processing.