a vector generation tester 12 generates test data as vectors and applies the test data to system under test 10 a capture interface 14 disposed between system under test 10 and vector generation tester 12 captures test data and sends the test data to a compression engine 16 compression engine 16 compresses the test data to reduce the space needed to save the test data in a compressed test data database 18 compression engine 16 may compress and save an entire test run or save a predetermined history of test run by overwriting compressed test data in database 18 once a predetermined number of cycles have passed or a predetermined portion of memory is used to save the test data if an error response is detected by tester 12 the test data is available for de compression by de compression engine 20 for analysis in a test environment for instance a logic analyzer 22 analyzes the test data to identify the stimulus that generated the error response by analyzing the test data history to separate stimuli applied to the defective portion of the system under test 10 from empty test cycles that did not apply stimulus a test program 24 is generated to apply stimulus that will generate the identified error response while reducing or eliminating empty test cycles 26 that are not associated with the error response with the de compressed test data available to logic analyzer 22 the test data history allows analysis of the manner in which erroneous data was written even if the data persisted on system under test 10 for a number of test cycles before being applied to generate the detected error response referring now to fig2 a system.