Yup, an .LDA loader wouldn't be hard. Excellent! I imagine you're busy with a soldering iron at this moment? :-) Once those are fixed, it will be interesting to see if the problems you saw with the OS's go away. It'd be easy to hack V6 to turn on parity error detection, if you'd like to. It will be interesting to hear those results... I don't know about 4116's, but I've seen a fairly high failure rate on _some_ cards with 256K DRAM's - on one board, a couple of chips totally dead, some others with just _some_ bad bits. Other cards were totally fine. I suspect it depends on the chip manufacturer. Could be - I'm not too familiar with the Fastbu. Ah... Looking at the "pdp-11/45 processsor handbook", 1972 and 1973 editions, there's an "Appendix E: Memory Parity" (of which I was previously unaware!), referred to in "2.5.6 Memory Parity". (I haven't checked to see if later ones have it.) It claims there are "16 memory status registers ... each one associated with an 8K section of memory". (It doesn't say whether UNIBUS memory, Fastbus, or both!) One bit in each register claims to be 'Halt Enable': "[when] set, the machine will execute a halt if a parity error occurs"; when clear, it traps to 4! Even better, it claims to be able to control whether the memory uses odd or even parity! (How, for UNIBUS memory, I don't know - there's no way to do this over the UNIBUS. And the MM11-L and MM11-U manuals indicate they both use odd parity, although there's a CSR bit to allow wriring 'wrong' - i.e. even - parity.) Very odd. Maybe this was deleted in the hardware (or they decided not to do it), and someone forgot to follow through in the manual? I recently found another reference to a /45 CPU feature I'd never heard of - forget what it was, alas! Could be. I wonder if there's any way to get ahold of the ECO list for that card? Noel