The Tandy TRS-80 Model 12 was a business system intended to replace the Model II which was widely used as an accounting and management system by numerous small companies.
Unlike Model II, it was a single board system with a white case instead of the typical dark grey one of previous TRS-80 models. It could be expanded by adding an optional card cage in which six expansion cards could be inserted, for example the monochrome high resolution card. However it was fully compatible with most popular Model II business programs.
The Model 12 was one of the first computer equipped with the new slim line 8" double side / double density floppy drive that could store 1.25 MB, twice as much as the Model II full-size version.
For faster operation, the main board could be exchanged with the 16-bit Tandy 68000 one. The computer thus became fully compatible with the Tandy Model 16 and so could run Unix operating system variants.