And just to bring you all up to speed (without forcing you to read every single post in these threads about this), I see the "strange artifacts" only a cold boot, during the 60 seconds it takes my SE/30 to check all 128MB of RAM (and yes, if I put in less RAM, they still appear, albeit less than 60 seconds as it takes less time to check less RAM). When the RAM check concludes, the "strange artifacts" vanish and the normal "gray" backdrop and happy Mac icon appear as actually booting begins.

Click to expand...

Haven't you just suggested the answer to your own question?

The SE/30 uses part of the system RAM for video, unlike the IIfx, so when you perform a cold boot with a IIfx ROM it will perform a full memory check. This memory check code has to be in the ROM (there is no OS at this point) but the IIfx ROM doesn't know that it shouldn't clobber the region used for video. After the OS starts to load, the system RAM used for video is protected from rogue activity and you see a normal screen again.

This is further supported by the fact that the artifacts only display on a cold boot and that their duration is linked to the length of the memory test. You may be able to confirm this theory by running a version of the Mac OS that allows you to disable the memory test on a cold boot.

The IIsi uses some system RAM as video RAM, but it requires more than a compact Mac. Additionally, it is likely that a different region of RAM is used for this purpose (the location should be in the developer notes or Inside Mac). So you should also get artifacts with a IIsi ROM, but they may be different.