It was a supported upgrade for VME Sun2s to swap the CPU board for a Sun3 and later a Sun4. This is why a lot of older VME cards from Sun were supported in the boot PROMs all the way through the SPARC machines. It's also why the ID PROM stayed pin-compatible all that time; you were meant to carry your old ID PROM forward when you upgraded so your MAC address and machine ID stayed the same and copy-protected software was happy. That finally ended with sun4c and SBus.
Wiki says the Atari TT's system bus was VME but it apparently wasn't brought out to any VME-compatible connectors.
Last edited by R. Belmont; 07/06/16 07:57 PM.