The TI-57 was a programmable calculator made by Texas Instruments between 1977 and 1982. There were three machines by this name made by TI, the first was the TI-57 with LED display released in September 1977 along the more powerful TI-58 and TI-59. It had 50 program steps and eight memory registers. Two later versions named TI-57 LCD and TI-57 LCD-II have a LCD display, but were less powerful (ran much slower) and had much less memory: 48 bytes to be allocated between program 'steps' and storage registers.
The TI-57 lacked non-volatile memory, so any programs entered were lost when the calculator was switched off or the battery ran out.
The LED display version of the TI-57 had a rechargeable Nickel-Cadmium battery pack BP7 which contains two AA size batteries and electronics to raise the voltage to the 9V required by the calculator. A popular modification is to power it from a 9V battery and use the battery cover of a LED TI-30 or a part of the dismantled battery pack. This modification provides a better battery life than the original battery pack.
Included, with at least the original version was a book entitled "Making Tracks Into Programming". It was self described as "A step-by-step learning guide to the power, ease and fun of using your TI Programmable 57".
Radio Shack also marketed this calculator, rebranded as the EC-4000.