> What's to stop you connecting up an old SIMM card? The memory won't be fast, but doable.
There aren't enough pins. Certainly not enough pins accesible in single-cycle reads/writes. Maybe you could multiplex them with external hardware to talk to a SIMM but you'd be talking to memory at single megahertz effectively.
An SDRAM controller in an FPGA on the other side of the QSPI link would be faster, but it'd still be slow. You could get it to work to say you've done it, but it'd run at literal-days-to-boot speeds.
The board (and chip) is meant and marketed for freetards who like Arduinos - so I bought one and so did several of my friends. LEDs were blinked and better futures dreamt of. It's cool. But it's not a workstation chip by any stretch of the imagination.
Hopefully the next version will have a real external memory bus.
Just for the records, you can run ELKS, a Linux variant for small processors, on 8086 hardware. Ages ago I successfully booted it on a 8088 based ancient industrial system with less than one megabyte of RAM and two floppy drives (hard disk? what hard disk?!? :). But the Linux a "normal" user would run is a very different thing which would require some more power.