Beta Disk Interface

[2] Beta 128 Disk Interface is a 1987[3] version, supporting ZX Spectrum 128 machines (due to different access point addresses).

Beta Disk Interfaces were distributed with the TR-DOS operating system in ROM, also attributed to Technology Research Ltd..

The first known USSR clones were ones produced by НПВО "Вариант" (NPVO "Variant", Leningrad) in 1989.

[5] Beta 128 schematics are included in various Soviet/Russian ZX Spectrum clones, but some variants only support two drives.

Phase correction of the drive data signal is also implemented differently.