TRS-80 Model 16B

Tandy later released the TRS-80 Model 16, as the follow-on to the Model II; an upgrade kit was available for Model II systems. The Model 16 added a 6 MHz, 16-bit Motorola 68000 processor and memory card, keeping the original Z-80 as an I/O processor. It could run either TRSDOS-16 or Xenix, Microsoft's version of UNIX. Of the two operating systems, Xenix was far more popular. TRSDOS-16 was essentially Model II TRSDOS, with no additional features and little compatible software. 68000 functionality was added as an extension, loading 68000 code into the 68000 memory via a shared memory window with the Z80.