To me, the most amazing thing about old systems was how little resources they needed to do useful work. The first version of Unix was designed to run on a machine with in 24KB (that's kilobytes) of core memory; even the famous and ubiquitous IBM System 360 was quite constrained by today's standards. "The software that controls what happens when you move your mouse on your PC — the mouse driver for Windows — takes more memory than all the NASA supercomputers put together had for Apollo," said Jones."[1]

That's right, they called them "supercomputers."

[1] https://www.techrepublic.com/article/nasas-unsung-heroes-the...

The very first of UNIX actually ran on a machine that couldn't even address that much memory, the PDP-7 has 13 bit addresses so you can only address 8k words of memory directly (1 word = 18 bits). The UNIX (or rather UNICS) kernel ran in 4k and left the other 4k for a user process; every context switch was a swap! If you want to try it out: https://github.com/DoctorWkt/pdp7-unix