Many of the ATMEL 8 bit chips do have an external memory bus. Not used in this case, but it's possible.
Sometimes it's pretty blurry what is a microcontroller and what is a microprocessor. The PIC32MZ/DA has an integrated Graphics Controller and 32MB of DRAM.
The AVR can't execute programs from the data bus, which means no execution from RAM or external memory, though you could write a virtual machine that could do so.
Sometimes it's pretty blurry what is a microcontroller and what is a microprocessor. The PIC32MZ/DA has an integrated Graphics Controller and 32MB of DRAM.