TI-81

• Name — TI-81 • Type — Graphing calculator • Entry — D.A.L. • Manufacturer — Texas Instruments • Introduced — 1990 • Discontinued — 1997 • Successor — TI-82 • Processor — Zilog Z80 • Frequency — 5 MHz or 6 MHz • Memory User — 2400 bytes of RAM • Display Size — 96×64 pixels, 16×8 characters • Precision — 13 digits • Prog Lang — TI-BASIC, Assembly • Supply — 4 AAAs, 1 CR1616 or CR1620 • Weight — 168 g • Dimensions — 6.8 x

The TI-81 is powered by a Zilog Z80 microprocessor, as used in the TI-73 and TI-81 to TI-86 graphing calculators. However, its processor is clocked at 2 MHz, whereas the others run at a frequency of either 6 or 15 MHz. It has 2.4 KB of user-accessible RAM, with additional RAM being allocated to the calculator's internal firmware. The calculator uses Texas Instruments' own in-house operating system, the Equation Operating System; the firmware used by all other Texas Instruments graphing calculators derive from this. The TI-81 can perform two-dimensional parametric graphing—in addition to standard two-dimensional function graphing, trigonometric calculations in units of either degrees or radians, simple drawing, the creation and manipulation of matrices up to a size of 6 by 6, and the execution of simple programs 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. Like most other Texas Instruments graphing calculators, the TI-81 is powered by four AAA batteries and one button cell backup battery; the backup battery ensures that programs loaded in memory are retained during battery changes. Some early TI-81 units omit the backup battery. Texas Instruments produced an emulator for the TI-81 and its Equation Operating System on a desktop computer; it is compatible with MS-DOS.