Burst Cutting Area.  This is a rarely used feature described in Annex K of the DVD physical specification that provides a bar code that is individually written to replicated DVDs in the area (22.3mm +0.0/-0.4mm and 23.5mm +/-0.5mm) inside of the lead-in area.  The BCA is created by a very powerful laser (Nd:YAG or CO₂) that burns and darkens the aluminum or other reflective metal layer in the center of the bonded DVD.  These marks have decreased reflectivity.  The marks are stripes, roughly 10 microns wide by 1200 microns long.  Discs can be given unique codes in this way.  The unique code could be used for copy protection or serialization systems.  This code contains up to 188 bytes.  Players read the BCA by rotating at a constant angular velocity (1440 rpm), moving the optical pickup to the BCA area, focusing on the information surface, and using a special decoding circuit (decoding the much lower frequency barcode signal than a normal DVD HF signal).  The marks are detected as a drop-out in the HF signal.  Because there is no player specification, support for reading BCA is not mandatory.  There is, however, a requirement for DVD-ROM drives to support the Mount Fuji specification, which includes a provision to read BCA info within the "read disc info" command.  With the exception of the ill-fated DIVX format, DVD Video players do not read BCA.  There are a few DVD manufacturers equipped to write BCA on replicated discs.