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 suport 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. TR-DOS handles SS/DS, SD/DD floppy disks.All modern versions support RAM Disk and some versions support hard disks.