I don't know what all this stuff means, but NASA paid Martin Marietta, where I worked back in those days, a LOT of dough, and provided documentation labeled Honeywell and showing pictures, though they were not relevant, of a model 516 computer. I spent six months or more poring over schematics, struggling to keep my eyes open, and making note of any potential race conditions, running logic simulations, etc, just to document all the potential single-point failure modes and their potential effect. We found several conditions which seemed to be "bugs" in the system, capable of creating catastrophic failures resulting in loss of lives and billions of dollars' worth of equipment, but those were "ground-ruled-out," meaning that, for example, a power supply failure in the mode wherein it drifts completely out of regulation, is a "normal" operating circumstance and need not be considered . . . but, I digress . . . The fact is, dladies and gentlemen, that the proposition of the time was that the engine controllers were Honeywell 516's, whatever that means. There was talk of installing a 68000-based computer in their place because semiconductor memories were faster, and a system of that type was superior for many reasons, not the least of which was modern read-only memories would allow much better testing. The plated-wire memories in use on the Challenger engine controllers allowed fault conditions which were not detected to be inherited from a previous mission, which risks went completely away with the newer design. It's not hard to imagine that such an upgrade would save on power and weight, as well as providing much more testability. It should also be enough faster to improve the system considerably. Dick ---------- <classiccmp(a)u.washington.edu> performed occupies consumes