[wroteafaq]

Either way with a switch, you will more than likely need to reset the EPROM, I had to do it when swapping chips from a R4K to a R3K and then back again.. if you search here on the forum you will find the command to do it.

Turns out that both the 3K and 4K behave the same way:  When you plug in a blank E^2 the CPU initializes it - everything but the MAC address, which is a deal-stopper, as it won't boot without a valid one (well, it boots, then panics).  But it's nice that it gets that far.  I found elsewhere discussions of how the 3K ROM monitor - but not the 4K - can be used to change the address, and that's fine, but a fussy difference.  So I'm just munging them in the Data I/O.

---

Whatever you do, make sure to not use an R4K CPU board in a system with an R3K-rated power supply. It may release magic smoke.

I speak from experience

Yeah, I picked up on the 4K using a higher power supply.  But letting out the magic smoke is not a very graceful way to respond to an overload condition; one expects in a quality system that the switcher would just shut down.