Atari 5200
The 1983 version of the Atari 5200 has two controller ports instead of four.  Atari changed back to the a simpler separate power supply and manual RF switch. It also had changes in the cartridge port to allow for the Atari 2600 adapter released that year. While the adapter was only made to work on the two-port version, modifications can be made to the four-port to make it compatible. In fact, towards the end of the four-port model's production run, there were a limited number of consoles produced which included these modifications. These consoles can be identified by an asterisk in their serial number.