It was a six-wheeled tank with a front-mounted blue photon beam headlamp, and a keypad on top. The toy could remember up to 16 commands which it then executed in sequence such as "go forward 5 lengths", "pause", "turn 15 minutes right (90 Degrees)", "fire phaser" and so on. There was a "repeat" instruction allowing simple loop to be performed, but the language was not Turing complete, lacking branching instructions; the Big Trak also lacked any sort of sensor input other than the wheel sensors.
There is now a small but dedicated Internet community who have reverse engineered the BIG TRAK and the Texas Instruments TMS1000 microcontroller inside it.
The American and European versions were noticeably different. The US version was moulded in gray plastic and labelled BIG TRAK whereas the British version was white and labelled 'bigtrak' with a different keypad.
Bigtrak also included an optional trailer accessory. Once hooked to Bigtrak, this trailer could be programmed to dump its payload.