The Mk2 is similar to the Mk1, but with the MicroSD reader mounted directly on the PCB rather than on a cable. People complained about the cable. They complained quite a bit, so I gave in and modified the design. I also switched from using an EPROM to a Flash chip. EPROMS have been obsolete for years and sales of the Mk1 board were good enough that sourcing chips was starting to become a significant headache.
The Mk2 sold exteremly well, to the point were I couldn't keep up with demand as it was quite fiddly to build. That prompted yet another redesign, resulting in the Mk3.
elksd.zip - a collection of Electron games, just unzip and copy to a MicroSD card
See the Mk3 Interface page for details.