The Dragon Plus was an add-inboard for the Dragon 32 or 64. It provided an additional 64KB of RAM and an 80 column text mode driven by an MC6845 with its own 2KB buffer. The board plugged into the SAM socket on the motherboard, with the SAM being placed on the Dragon Plus board and also required one of the BASIC roms to be moved to the Dragon Plus board with a ribbon cable plugging into the vacated socket. The 80 column display required an additional monitor socket to be provided on the Dragon case as this used its own composite video output circuit.
There was also an IDE interface planned to allow connection of a hard disk drive - the 40-pin header for the IDE interface can be seen on the Dragon Plus circuit board, along with what appears to be space for a missing IC.
A special version of Edit+ was available, along with drivers for OS-9 Level 1 and a special version of Flex. Both the OS-9 and Flex implementations used the additional 64KB as a RAM disk so the main OS ran completely from RAM, thus speeding up operating and allowing disk 0 to be changed. Both OS-9 and Flex also supported the use of the 80 column display.
A near replica of these boards was launched in early 2019 by John Whitworth, with the approval of Ted Opyrchal, ex-MD of Compusense. The boards are functionally identical though they do not have the empty expansion pinout at the bottom, which was never utilised anyway. The boards can be purchased, in kit form, here.