Back then, fitting in RAM was a big problem: The PDP-11 (the first kind of computer to run Unix, as opposed to UNICS) had a 16-bit address space, which gives yo

Back then, fitting in RAM was a big problem: The PDP-11 (the first kind of computer to run Unix, as opposed to UNICS) had a 16-bit address space, which gives you 64 K of RAM if you ignore the fact peripherals were memory-mapped and so took addresses away from actual memory. Later models had split I+D, or separate address spaces for Instructions and Data, but that's still only 128 K. https://gunkies.org/wiki/PDP-11_Memory_Management https://gunkies.org/wiki/PDP-11_Memory_Management