The first graphing calculator made by Texas Instruments.
Differences in Programming
The 81 has fallen out of common usage (designed in 1991). It is underpowered, although it is powered by the Z80 microprocessor. This is the same processor used in the 8x series calculator, with the exception of the 89. The 81 only runs at 2mHz, while the other ones run at 6-15 mHz.