The ATmegas only go up to 16KBytes RAM, with 4KBytes or less being usual. As a Harvard architecture device, none of your binary is memory-mapped, which can make porting existing code a bit annoying. sizeof(int)==2, which doesn't help either (however sizeof(void *)==2 as well, so there is at least that).

It's rather unusual by today's standards. Certainly quite different from an ARM.