The actual computer that contains and runs the game data is on one of many different types of PCBs. These can be found in the back of the machine and are often hooked up to the amp unit, lights, JAMMA harness, monitor, and other parts of the cabinet.
The System 573 is a PlayStation-based board. Depending on which optical drive is installed, it can play DDR 1st through Extreme.
Python 1 is a PlayStation 2-based board. It only has support for Dancing Stage Fusion. This and all newer boards usually require an EXT-IO, a separate board that translates JAMMA signals from the cabinet into ones that the PCBs can understand.
Python 2 is a box that contains a PlayStation 2. It also contains USB I/O board commonly referred to as a P2IO. It supports SuperNOVA 1 and 2. Interestingly, by enabling a DIP switch and jumping a few pins, the Python 2 can boot without the need of an EXT-IO, although it will be unable to recognize input from individual sensors.
Bemani PC, this version often referred to as “Type 4” or “Dragon”, is a Windows-based PC that can run DDR X through A20. It is distinct from other models of Bemani PC by its Radeon HD 2400 GPU. Depending on the cabinet, these boxes contain a P3IO board (which supports JAMMA input) or a P4IO (for white cab connectors), which translate cabinet signals to USB.
There is a newer Bemani PC, sometimes referred to as “Type 5” or “Type 6” depending on where you look. Originally released with DDR A, it also runs A20.
Roxor released several variants of “Boxor” PCs for running In The Groove and In The Groove 2. Kits meant to run in DDR cabinets contain an I/O board called an ITGIO which translates JAMMA signals.