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.