TI-86 is a programmable graphing calculator introduced in 1997 and produced by Texas Instruments. The TI-86 uses the Zilog Z80 microprocessor. It is partially backwards-compatible with its predecessor, the TI-85.
The TI-86 can be thought of as the tier among various Texas Instruments calculators directly above the TI-83 and TI-84 line. In addition to having a larger screen than the TI-83, the TI-86 also allows the user to type in lower case and Greek letters and features five softkeys, which improve menu navigation and can be programmed by the user for quick access to common operations such as decimal-to-fraction conversion. The calculator also handles vectors, matrices and complex numbers better than the TI-83. One drawback, however, is that the statistics package on the TI-83 range doesn't come preloaded on the TI-86. However, it can be downloaded from the Texas Instruments program archive and installed on the calculator using the link cable." (Wikipedia)
Download Texas Instruments TI-86 - BIOS (TOSEC-v2006-04-21):
Direct Download Link: TI-86 - BIOS (TOSEC-v2006-04-21).rar