The Exatron Stringy Floppy (or ESF) is a continuous loop tape drive developed by Exatron. The company introduced an S-100 stringy floppy drive at the 1978 West Coast Computer Faire, and a version for the Radio Shack TRS-80 in 1979. Exatron sold about 4,000 TRS-80 drives by August 1981 for $249.50 each, stating that it was "our best seller by far". The tape cartridge is about the size of a business card, but about 3⁄16 inch (4.8 millimetres) thick. The magnetic tape inside the cartridge is 1⁄16 inch (1.6 millimetres) wide. There is no single catalog of files; to load a specific file the drive searches the entire tape, briefly stopping to read the header of each found file. The tape loop only moves in one direction, so a file that starts behind the current location cannot be read until the d