The TI Operating System, made by Texas Instruments for their graphing calculators. This is the software that is needed to run the calculator. Much like the kernel for Linux and Windows systems, the TIOS handles all the components of the calculator hardware and gives the user an interface to work with. This software is stored in a Flash EEPROM chip in the calculator. The contents of the chip can be changed, which means that the calculator is upgradeable, but the contents cannot be changed on the fly like normal RAM. The TI-Graph Link must be used to send the new operating system to the calculator.