This gives a peek at the software running behind the Western Technologies Development Card for uploading (they call it downloading) from the PC to the Mega Drive. SEGALOAD sends the game image through the PC’s parallel port into SRAM on the development cartridge. Beats having to burn the EPROMs with the game code every time you update code!

It reminded me of a Mega EverDrive. The 2012 Mega EverDrive could load a ROM from SD or transfer one from a PC over USB into cartridge memory. Different hardware, but a similar way to get new code running on the Mega Drive.

Sources