TI-81

Features

The TI-81 is powered by a Zilog Z80 microprocessor, like those used in almost every other Texas Instruments graphing calculator (except the TI-80, TI-89, TI-89 Titanium, TI-92, TI-92 Plus, Voyage 200 and TI-Nspire series). However, the processor is clocked at 2 MHz whereas the other Z80-powered Texas Instruments calculators run at speeds of at least 6 MHz (the TI-83 Plus Silver Edition, TI-84 Plus, and TI-84 Plus Silver Edition can run at 15 MHz). It contains 2400 bytes of user RAM, with additional RAM used internally by the calculator firmware software system.

The TI-81's user interactions are provided by its so-called Equation Operation System. This is comparable to the interface provided by the more recent TI-82, TI-83, and so on. This system is capable of such tasks as two-dimensional parametric graphing (in addition to standard two-dimensional function graphing), trigonometric calculations in units of either degrees or radians, simple drawing capabilities, creation and manipulation of matrices up to 6x6 in size, and programming in a proprietary statement-based language.

In late 2009 an exploit was found that can be used to execute machine code on the TI-81, using manual input of code. The TI-81 has no data link interface; its only means of input and output are the keyboard and screen.

As with its successors, the TI-81 is powered by four AAA batteries and one CR1616 or CR1620 lithium backup battery (to ensure programs are persistent when the AAA batteries are being changed). Some early TI-81 units omit the backup battery; if the AAA batteries of one of these units are changed one at a time and quickly, the memory contents are still retained.

Texas Instruments distributes software which emulates the TI-81 and its Equation Operating System on a desktop computer using DOS or DOSBox.