The Exatron Stringy Floppy (or ESF) is a continuous loop tape drive that was developed by Exatron for use with the Radio Shack TRS-80 microcomputer, among others, and was launched in 1979. The tape cartridge is about the size of a credit card, but about twice as thick. The magnetic tape itself was 1⁄16 inches (1.6 millimetres) wide.
According to Embedded Systems magazine the Exatron Stringy Floppy used Manchester encoding, achieving 14K read-write speeds and the code controlling the device was developed by Li-Chen Wang (who also wrote a Tiny BASIC, the basis for the TRS-80 Model I Level I BASIC.)
In the July 1983 issue of COMPUTE!'s Gazette the ESF for the VIC-20 and the Commodore 64 was reviewed. The April 1983 issue of Creative Computing reviews the Winter CES show where Texas Instruments showed the TI Compact Computer 40 (CC-40) which included an optional peripheral, "a wafertape digital tape drive similar to the Exatron Stringy Floppy ($139)."
Exatron pitched the ESF as "The viable alternative". The ESF was faster and more reliable than a data cassette, and half the price of a floppy disk.