[pups] Unix and PDP11/20 (was PDP9?)

As Billquist, Wilson and others pointed out, the first versions of Unix did run on machines with no memory mapping or protection, and indeed context-switching was accomplished by swapping. By 1973 we had the luxurious 11/45, to considerable relief. I'm not positive about the logo on our first PDP-11. On the earliest handbook I have, the front panel photo just shows "PDP11", though inside the handbook it does talk about the two models (11/10 and 11/20). Both had the same KA11 processor, but the basic 11/10 sported 1024Kw ROM memory plus a generous 128 words of RAM, while the 11-20 had 4096Kw core RAM, and the ASR33 Teletype was included. You could add more RAM to the 11/20. Incidentally, the machine's handbook was a wonder. In 104 pages (each 5.25x8 inches), it described the whole system: not only the instruction set but the theory of the Unibus (including some logic diagrams) together with programming specifications for the TTY, the clock, and the paper tape reader. Dennis