TRSDOS

TRSDOS (which stands for the Tandy Radio Shack Disk Operating System) is the operating system for the Tandy TRS-80 line of eight-bit Zilog Z80 microcomputers that were sold through Radio Shack from 1977 through 1991. Tandy's manuals recommended that it be pronounced triss-doss. TRSDOS should not be confused with Tandy DOS, a version of MS-DOS licensed from Microsoft for Tandy's x86 line of personal computers (PCs).

With the original TRS-80 Model I of 1977, TRSDOS was primarily a way of extending the MBASIC (BASIC in ROM) with additional I/O (input/output) commands that worked with disk files rather than the cassette tapes that were used by non-disk Model I systems. Later disk-equipped Model III computers used a completely different version of TRSDOS by Radio Shack which culminated in 1981 with TRSDOS Version 1.3. From 1983 disk-equipped TRS-80 Model 4 computers used TRSDOS Version 6, which was a development of Model III LDOS by Logical Systems, Inc. This last was updated in 1987 and released as LS-DOS 6.3.

Completely unrelated was a version of TRSDOS by Radio Shack for its TRS-80 Model II and TRS-80 Model 12 professional computers from 1979, also based on the Z80 and equipped with 8-inch disk drives. The later machines in this line, the Models 16 & 16B and Tandy 6000, used the Z80 as an I/O processor to its main Motorola 68000 chip when running operating systems on the 68000, and could run the Model II version of TRSDOS for backwards compatibility with older Z80 applications software. When running the older Z80 operating systems, the 68000 was unused.