That's 64KB, right? DEC used to talk of PDP-11 memory in words, back in the day, so it's never quite clear unless the 'B' or 'W' is specified. Anyway, 64KB out to be enough to run most things. I have't looked to see how big a system with just RL and DL drivers, and a minimum number of disk buffers (that's probably the easiest way to get the size down almost as far as it will go) is, but it's probably in the region of 30-35KB (20KB text, and 10-15 KB data). That leaves plenty for user processes (not max sized, of course). Oh, so that must have been 64KW - 128KB. That will give you plenty of room for a decent-sized kernel, and user processes. Wonder why it won't boot, then? Anyway, those are pretty rare. I have a couple of spare M7847's; they're only 32KB, but they'd help. You've got a couple of spare hex MUD slots now in the DD11-C, right? Speaking of which, where is the M7891 plugged in? It couldn't go in the DD11-B, or in the CPU backplane? Sorry, need exact details: after the '!' prompt, anything you type kills the system on the first character? Or only "rlunix<CR>" does? How about "foobar<CR>"? I'd have to look at the bootstrap source, but I think typing a non-existing file name should take you back to the top-level prompt. Noel