-= General Information =-
Announced in 1990, the TI-81 is the first graphing calculator TI released. With only 2400 bytes of program memory (a drastic improvement over the Casio fx-7000G's 430 bytes) and limited mathematical capabilities, the TI-81 was designed as an entry-level graphing calculator.
The TI-81 saw six notably distinct revisions. The initial TI-81s produced before May 1991 lack a bar underneath the [ON] button, and has a circular indentation where the backup battery would be found in later models. Models produced between May 1991 and January 1992 do not use a backup battery, and have a flat plastic cover over the backup battery area. The molds for the backup battery were being used (presumably in preparation for the TI-85's release and TI-81's upgrade), and although the backup battery's space and labeling are underneath the plastic cover, the contacts on the mainboard are missing. In February 1992, hardware revision 'A' entered production, adding the backup battery. Just two months later, in April 1992, hardware revision 'B' was introduced, bringing with it a drastically improved screen akin to that of the TI-85 while retaining the 96x64 pixel display resolution. Furthermore, 'B' revised the display bezel to be evenly textured over the entire screen cover, as the original screen cover was prone to scratching and caused annoying glare. Sometime between March 1993 and July 1993, the TI-81 was completely overhauled to minimize costs and use TI-82 components. The display type was reverted back to the original, low-contrast display; the color of the calculator was changed from a grayish blue to a dark blue; the new ROM version V2.00 appeared; and internally, the calculator uses a TI-82 mainboard and display drivers. Shortly after the introduction of the TI-82, the display bezel was updated to match the styling of the TI-82, and ROM V2.0V was introduced alongside that change. The final revision of TI-81 was released in 1995, and updated the display bezel to match the styling introduced in 1995; the TI-85 and TI-82 also saw this change.
The TI-81 was generally replaced by the TI-82 in 1993, and was discontinued at the beginning of 1997 after the introduction of the TI-83.
-= Specific Examples =-
First-Generation:
0719871 I-0790 pre-'A', ROM 1.1 (first revision)
1210793 I-1292 'B', ROM 1.8K (third revision)
Second-Generation:
0804828 I-0893 'D', ROM V2.00 (fourth revision)
17050114 I-0594 'F', ROM V2.0V (fifth revision)