A portable, programmable, microprocessor-controlled, universal field test unit is provided which is capable of performing functional tests on most, if not all, of the better known present-day disc drives, including the 80, 160 and 300 megabyte types. The unit to be described will be termed herein as a programmable disc drive qualifier, and it is capable of carrying out a wide variety of special test programs, as well as standard diagnostic programs, and it may also be used to format disc packs with many different formats, including thirty-two and eighty-six sector formats. The qualifier may be internally set to count all data errors, or only uncorrectable errors. The qualifier, in the embodiment to be described, is controlled by a combination of twelve operation keys and twelve numeric keys. A complete instruction is generated by the actuation of one of the operation keys and one of the numeric keys. Individual instructions may be executed in the unit, or it may be run automatically under program control. Programs may be created by the actuation of the operation keys and numeric keys, or they may originate from a pre-programmed memory.