Beta Disk Interface is a disk interface for ZX Spectrum computers. It was developed by Technology Research Ltd. (United Kingdom), in 1984 and released in 1985 with price £109.25 (or £249.75 with one disk drive). Beta 128 Disk Interface is a 1987 version supporting ZX Spectrum 128 machines (difference is in access points addresses). Beta disk interfaces were distributed with TR-DOS operating system in ROM, also attributed to Technology Research Ltd. Latest firmware version is 5.03 (1986).The interface was based on the WD1793 chip.