The first one I bought (a PDP-11/35 in a Tektronix SPS system) was
56K bytes of *core*. They didn't make 512byte planes, nor did they
make 512KB PDP-11s, AFAIK.
I started timesharing with a PDP-11/20 with, I think, 32K words (64
kbytes) of core, moved up to an 11/45, and, by the time they fired me,
was running RSTS/E timesharing on a PDP 11/70 with 256k words of
cached dram, a bunch of big disk drives, magtape, DecTape, card
reader, paper tape reader/punch, line printers, modems, and a
full-time operator. We even interfaced an IBM 029 keypunch machine.
The RSTS os would run in native mode or would emulate the RSX-11 or
RT-11 operating systems perfectly.
We bought scores of PDP-11s for pipeline control systems, mostly run
under the REX rtos authored by, um, me.
John