Oh wow. I haven't thought of a PDP-8 since... Ah... 1990's some time. Our secretaries all had PDP-8's embedded in a dedicated word processor which name escapes me. IIRC it had another odd word size: 12-bits. I inherited several of those when we moved out of our lovely old futuristic FCRC building in McLean, VA and into a boring run-of-the-mill 6 story block in Vienna, VA. I also inherited a bunch of DEC bidirectional daisy-wheel printers. Both the printers and the PDP-8's were built like tanks.I'm betting you're actually thinking of a PDP-8. The PDP-20 was relabeled as the DECStation 20 before release.
I used a PDP-8/L with 4K of RAM in high school. It didn't have any disk capacity at all. Everything was stored in RAM and when it was turned off, everything was lost.
This is my memory of the PDP-8. One of my classmates could actually paddle in the bootstrap from memory!
The last time I saw a PDP-8/L, it was part of an retired scoreboard setup in a university's main gym ("Slats" Gill Coliseum at Oregon State University).
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I do believe my research data-capture computer was a PDP 11/20. It just said "Programmed Data Processor" on the front, so I may have gotten the number part wrong. We also had a bunch of PDP 11/45's and my personal favorite, the PDP 11/34. I see I left the "11/" off above. Sorry about that. Failing memory.