The TI 73 series is a series of graphing calculators made by Texas Instruments, all of which have identical hardware. The original TI-73 graphing calculator was originally designed in 1998 as a replacement for the TI-80 for use at a middle school level. Its primary advantage over the TI-80 is its 512 KB of flash memory, which holds the calculator's operating system and thereby allows the calculator to be upgraded. Other advantages over the TI-80 are the TI-73's standard sized screen, the addition of a link port, 25 KB of RAM, and a faster 6 MHzZilog Z80 processor. The TI-73 also uses the standard 4 AAA batteries with a lithium backup battery. In 2003, the TI-73 was redesigned with a sleek new body shape and redesignated the TI-73 Explorer to indicate its currently intended use as a bridge between the TI-15 Explorer and similar calculators and the TI-83 Plus, TI-84 Plus, and similar calculators. Later, the TI-73 Explorer was remodeled to resemble the TI-84 Plus graphing calculator more closely. Due to lack of demand in middle schools, the TI-73 and TI-73 Explorer have not been huge sellers for TI and are not carried by most retail stores. Most American upper-level middle school algebra courses generally tend to use the TI-83 or TI-84 families instead of the TI-73 or TI-73 Explorer, while most basic middle school math courses generally do not use graphing calculators, instead opting for scientific calculators such as the TI-30 or TI-34 families. Originally the TI-73 could only run programs written in TI-BASIC, although that has changed in recent years. In 2005 an assembly shell called Mallard was released for the TI-73. Mallard allows the user to run programs written in assembly language. As with the TI-82 and the TI-85 before, a hacked backup file is downloaded containing the assembly shell. Released in late 2008, the Windowsutility Chameleon allows a user to load the TI-73 Explorer with a slightly modified TI-83+ firmware, giving it nearly equivalent functionality. In 2009, Texas Instruments updated the skin of the TI-73 Explorer to match the shape of the larger TI-84 Plus's case. This resulted in a slight increase in mass from 182 grams to 208 grams. The hardware and software remained unchanged and is identical to an older unit wearing the TI-83 plus style casing.
