Texas Instruments TI-81

Datasheet legend
Ab/c: Fractions calculation
AC: Alternating current
BaseN: Number base calculations
Card: Magnetic card storage
Cmem: Continuous memory
Cond: Conditional execution
Const: Scientific constants
Cplx: Complex number arithmetic
DC: Direct current
Eqlib: Equation library
Exp: Exponential/logarithmic functions
Fin: Financial functions
Grph: Graphing capability
Hyp: Hyperbolic functions
Ind: Indirect addressing
Intg: Numerical integration
Jump: Unconditional jump (GOTO)
Lbl: Program labels
LCD: Liquid Crystal Display
LED: Light-Emitting Diode
Li-ion: Lithium-ion rechargeable battery
Lreg: Linear regression (2-variable statistics)
mA: Milliamperes of current
Mtrx: Matrix support
NiCd: Nickel-Cadmium rechargeable battery
NiMH: Nickel-metal-hydrite rechargeable battery
Prnt: Printer
RTC: Real-time clock
Sdev: Standard deviation (1-variable statistics)
Solv: Equation solver
Subr: Subroutine call capability
Symb: Symbolic computing
Tape: Magnetic tape storage
Trig: Trigonometric functions
Units: Unit conversions
VAC: Volts AC
VDC: Volts DC
Years of production:   Display type: Graphical display  
New price:   Display color: Black  
    Display technology: Liquid crystal display 
Size: 6"×3½"×½" Display size:  pixels
Weight: 10 oz    
    Entry method: Formula entry 
Batteries: 4×"AAA" alkaline + 1×"CR-2016" Lithium Advanced functions: Trig Exp Hyp Lreg Grph Cmem Mtrx BaseN 
External power:   Memory functions:  
    Programming model: Formula programming 
Precision: 13 digits Program functions: Jump Cond Subr Lbl Ind  
Memories: 2400(0) bytes Program display: Formula display  
Program memory: 2400 bytes Program editing: Formula entry  
Chipset:   Forensic result:  

ti81.jpg (27494 bytes)The TI-81 is an earlier member of Texas Instrument's current graphic calculator family. It has 2400 bytes of user memory for storing programs and variables. Programming the TI-81 is very similar to programming Casio calculators. Even their limitations are very much alike: for instance, in the TI-81, just like on the Casio CFX-9800G, I have not found a way to use the results of a user program (not just a simple expression) for building a graph. (Then again, since I don't have a TI-81 manual, maybe I am just missing the obvious somewhere.) In any case, I'm wondering whether these similarities are merely a coincidence.

Here is what a program that calculates the Gamma function for any real argument looks like on the TI-81:

:Input X
:Lbl 1
:If X>=0
:Goto 2
:Goto 1
:Lbl 2
:e^(ln ((1+(76.18009172+9.5E-9)/(X+1)
  +(X+.5)ln (X+5.5)-X-5.5)/Y->Y
:Disp Y