A
graphing calculator made by
Texas Instruments that is a big improvement upon the
TI-81 and was improved upon by the
TI-83.
To find out your memory version, from the Mode screen, hit Alpha-S. Under the question will be a number. Then press any key besides Enter (Enter will reset your calculator's memory.) The memory versions I've seen are: 17.0, 18.0, 19.0, and 21.0.