The PET 4000 series computers featured several improvements over the earlier 2000s. They had more memory and an improved graphics system. The 4000s, unlike the 2000s, did not slow down drastically when graphics were displayed on-screen.

The 4000s were infamous for the fact that, by entering a specific command, the user was able to accelerate the video chip to the point that it melted down and destroyed itself. This became known as the "killer poke."

The PETs were unique in that their cases opened like an automobile hood. Since the monitor was attached to the case, this could be an awkward procedure.