Systems comprising a wire and an excision instrument particularly intended for breast biopsy are provided. It comprises a housing; a scanning device; a pre-scan assembly generating a light beam and directing the light beam toward the scanning device; and a post-scan optical assembly receiving a scanning beam reflected from the scanning device and causing the beam to traverse a photoconductive member along a scan path. The apparatus further includes a position sensor that senses a position of the grinding surface along an axis approximately normal to the working surface and a controller that receives a position signal from the position sensor and transmits a control signal to the feed mechanism in response to the position signal. A fully hidden refresh mode allows for timely refresh operations while operating in cache line mode. The computer system is rebooted.