Abstract: Disclosed herein is an apparatus for testing a digital device. The apparatus includes a generator adapted for connection to the device under test for generating a controlled data stream in words. The generator transmits the controlled data stream to the device which in turn transmits the controlled data stream to a detector. The detector is adapted for connection to the device and receives the controlled data stream. The detector compares the controlled data stream to an expected result and identifies each unexpected result as an error event. The apparatus includes a computer which records the location information of each error event and performs statistical and distribution analysis to allow a user to obtain through high resolution graphical display information used to diagnose the performance of the tested device. The computer controls the input and output of data from the device under test.