So, back in the stone age, computers came with serial ports to communicate. These were trapezoidal connectors with 9 pins. Computrainers came with stereo to 9 pin adapters. These were simple, really just a 9 pin serial connector with a stereo plug stuck in one end and 3 wires connected between them.
Before long, traditional serial ports gave way to USB (Universal Serial Bus) ports. Computrainer started selling adapters. These had a 9 pin serial connector at one end and a USB connector at the other, and the necessary circuitry to adapt the raw serial data to USB. This is where the FDTI 'chipset' comes it. It seems that the FDTI chipset worked better, or was the only one that worked. They even had 8 port versions, so you could connect 8 Computrainers to a single computer. This was a boon to the Computrainer 'labs' around the country. This required 2 adapters, the stereo to 9 pin, and then the 9 pin to USB. Eventually, they created a single adapter that went from stereo directly to USB. These were custom, and are relatively rare. I don't think the current 'stereo to USB adapters' you see for music/headphones will work.
When you first turn your Computrainer on, you should see a number, that is the firmware version. In the past, you could order an upgrade from Computrainer. This was an actual new chip for inside the handlebar controller.
This is kind of what the stereo to 9 pin adapters looked like:
