A2000-A
The first version of the A2000 was designed by a group in Germany. It shares much of the A1000 design, integrating several parts of the motherboard design. The system was based upon an interesting design but was restricted in many ways:

the thin Agnus could only use 512 Kb RAM
the machine was unreliable representing a refinement of 1985 technology rather than an advancement. For example, the CPU card slot was an internal version of the A1000 external edge connector and the video slot was an internal version of the external video port.
Later models were extended with digital video signals and some parallel port lines.

A2000-B
The redesigned motherboard abandoned the German improvement on the A1000, instead developing an American designed cost reduced version of the A500. These are generally referred to in the UK as the B2000.( You can check the version you have by looking in the lower left hand corner. The later A2000 motherboard are marked "B2000-CR". The original A2000's are marked on the left side with "©1986 COMMODORE", "AMIGA 2000" and "MADE IN GERMANY (BSW)).

As part of the cheaper design the control logic for the expansion bus is integrated into the Buster and the 68000 and 1 Mb memory are moved onto the motherboard. . The video slot is extended with more signals and the CPU slot has a coprocessor interface. Early versions of the B2000 shipped with Kickstart 1.2, later ones with version 1.3.

The A2000-B design forms the majority of the number of A2000s sold.

A2000-C
The final version of the A2000 is based upon the improved ECS Chipset, but otherwise identical to the 2000b. It is also known as the Amiga 2000+ in the US. This revision shipped with the new improved Kickstart 2.04.