Massive. NERVES requires Linux, plus system libraries. I've built RTEMS applications in the tens of kilobytes. Both require BEAM, of course, plus the actual Erlang application itself.

Nerves is around the 10-20 MB range. The main downside of the Grisp system I could see would be that nerves has a really nice two phase firmware update story, and that isn't mentioned in Grisp that I've found. IMHO, the remote firmware update and tooling is a "killer" feature of nerves.

Firmware update in the field is important but only a small aspect of a embedded system (one that really needs to work).

But Erlang already offers a lot around releases out of the box and in our case The VM + the whole "OS" is just one file to swap so we don't have a lot of problems one has if Linux + Erlang + Application needs to be updated.

FWIW: for larger Embedded systems we use FreeBSD + nanobsd wich solves a lot of the above mentioned problems. Update image verification and running the update is about 200 lines of Erlang code. And nanobsd comes with the normal FreeBSD system (builds disk/flash filesystem images with multiple partitions for easy update -- runs from one swap to the other)

> Both require BEAM, of course, plus the actual Erlang application itself.

Exactly - that part is not tiny, so I wonder what the two look like in comparison.