A high resolution thermal printer capable of printing both directly on a thermally responsive media and indirectly through a thermally responsive donor media is disclosed. The printer has a printing media guide mounted as an intermediate clamshell structure to accurately position the printing media immediately adjacent the print head and platen. The printing media guide includes a nip roller and guide bar independently suspended on a spring biased, pivot plate arrangement. The printing media is centered on the supply spool, and the printer includes a read/write circuit to communicate with a profiler chip centrally mounted in the printing media roll. The printer may also include a read/write circuit to communicate with a donor profiler chip centrally mounted in the donor media roll. A constant pressure brake with a friction belt is used directly against the printing media. A spring arm latch/channel block arrangement is used to secure the printing media supply spool. An optical sensor and return motor on the supply spool are used in accurately positioning the printing media for subsequent color passes during full color printing.