The black version requires that the linking software toggle the serial port lines directly. The gray version uses standard serial protocol and converts it to the TI linking protocol inside the Graph Link. Both use the serial port and only differ in how the computer interfaces with the calculator. The classic TI-Graph Link, an official link cable, comes in both "black" and "gray" colored variants. Obtain a serial cable, which is slightly harder to build than the parallel
If you don't have a free parallel (printer) port, you might find it better to The homemade parallel cable is the cheapest to buy or build, and has more supported linking software than the serial link. Homemade cables such as the serial link or PICLink also exist but are no longer cost-effective for most users and are limited to older calculator models. If you have an older computer with serial ports, the TI Graph Link will work with most calculators. For most other calculators, the silver link (TI Connectivity Cable USB) is your best choice. For newer calculators that include the direct USB cable, that is your best choice. If you have a PC, you have several choices. Otherwise, the TI Connectivity Cable USB is the best choice for modern Macintosh computers (which have USB ports but no serial/parallel ports). If your calculator came with the direct USB cable, that is recommended. If you have a Macintosh, your only choices are the TI Connectivity Cable USB, the USB direct cable, or the cheaper, build-it-yourself PICLink. Lastly, you can make a homemade cable yourself. TI also still produces its older serial cables, the TI Graph Links ("black link" and "gray link"). TI's newest calculators can also use a direct USB cable ("TI Connectivity Standard A to Mini-B USB Cable") which is included with the calculator.
The most common method is via the TI Connectivity Cable USB ("silver link") which works with most calculator models. There are several ways to link to a computer. For linking to a computer, a separate cable is required (which may be included with your calculator as well depending on the model). All TI graphing calculators include a calculator-to-calculator link cable.