[EE hat-on] Until I hear a classier diagnosis: the beeps/other noises signalled even-moi that, this was: irregularly-irregular, indubitably signalled much-moar than 'an App gone all Orange'. That the usually rock-solid 'Coldish' re-boot' failed to cure made more evident that [The OS] itself was-STILL-bollixed despite: all experience of the Niceness of the "Save a mirror/regularly"--built. in.

Thus, whatever 'caused' the Colonel er. kernel to self-destruct, short of Colonel-panic: WAS not found/Noticed by the almost-bulletproof loading of that Image, STILL after thrice attempts: It ain't magic, but guts-level 'lectronics as seemed cause the clusterfuck. My mere/brief Cold-shutdown was Not Enough. (I should have unplugged for 10+ minutes in first place, but s l o w learner sometimes).

Capacitors store charges for t = a ƒ(the hi-Ω value) bleeder resistors decided on design. I know not just What-items on the mobo are Always Live (only presumably.. deadened via the unplug "for a trice"). I wonder if anyone here knows enough re the Electronics-within that mobo: just What is the e- diagram, the logical-flow-chart? of the Always-On pieces of this proprietary design, whose full schematic shall never reach our eye-pans. Anyway, my diagnosis fits the above; it worked and I see no cubic-closest-packed SImpler one; does anyone else?

tll;drr--unless it proves an intermittent-Thing--{worst-case for All troubleshooting, evah}--whence I get to really Test the postulate: it's a oddly-flaky component in AlwaysOn stuff or a fucking Cosmic-Ray Strike, for my money..

And I am unanimous in that. (Today) ..so if you Crash-off yer ailing iMac for whatever reason -- w a i t 10 -- make it fifteen even, if you want to cover all bases; Evidence! ... 1 datum. :-þ