Being mildly curious, I fed '26 3 ^p' into 'dc' to see just how big it was - and got "17576", a 16-bit word array of which would fit into a PDP-11 64KB address space. I think the answer is in the first line - V3 didn't use the PDP-11 memory management, so the kernel _and_ the application had to fit into 56KB. So there may well have not been 36KB available to hold a 26^3 array of 16-bit words. The other possible explanation is that it was perfectly possible to run UNIXes of that era (V4 on) on machines without enough main memory to hold the kernel and a 'full-sized' process simultaneously. (Our original machine, an -11/40, started out without a lot of memory; I don't recall exactly how much, though. It had, I'm pretty sure, 3 banks of core; I was thinking it was 3 MM11-L core units, which would be 3x16KB, or only 48KB, but my memory must be wrong; that's not really enough.) Noel