TR-DOS is a disk operating system for the ZX Spectrum with Beta Disc and Beta 128 disc interfaces. TR-DOS and Beta disc were developed by Technology Research Ltd (UK), in 1984.
It became a standard, and most disk releases for the ZX Spectrum, especially of modern programs are made for TR-DOS as opposed to other disk systems. Current emulators support TR-Dos disk images in the formats .TRD or .SCL. A clone of this interface is also used in the Russian Pentagon and Scorpion machines.
The latest official firmware version is 5.03 (1986). Unofficial versions with various enhancements and bug-fixes have been released since 1990, with the latest being 6.10E (2006).
TR-DOS handles SS/DS, SD/DD floppy disks. All modern versions support RAM Disk and some versions support hard disks.