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 . the computer includes a data bus for enabling communication between the computer and the generator and for enabling communication between the computer and the detector .