TOM ELLARD MEETS THE PDP-12 AT THE LIVING COMPUTER MUSEUM

Published on Sep 24, 2015 Redmartian

"Tom was introduced to the PDP-12 while Stephen Jones was working through the restoration effort in the summer of 2013. Stephen sent videos to Tom and it made an appearance in the interactive fiction game [H.H.] Here Tom is experiencing the PDP-12 for the first time running a program called Kaleidoscope in which the user manipulates two dials (X and Y) which are then sampled and used in producing the image on the screen. The -12 has a speaker and every time accumulator 0 is used a flip flop generates a pulse or square wave. Based on how quickly this occurs you will usually hear this square wave in the audio range. The speaker has been amplified for this video."

I asked Red Martian when the PDP-12 came out and how it produced audio:

"1971, though it goes back to the LINC and LINC-8 computers starting in 1960. It has an analog to digital converter which can sample from 8 multi-turn pots and 8 1/4" jacks as well as a bank of 6 relays for switching things. The tone you hear is a flip flop producing a square wave at a frequencing in the audio range everytime accumlator 0 is used. So depending on how busy the system is doing the calculations for plotting points on the X/Y display in kaleidoscope you get a different frequency, sometimes FMish sounding.

I bypassed the speaker and wired in an amplifier for the sake of Severed Head's visit."

PDP stands for Programmed Data Processor. Wikipedia has page on it that goes through the history of the PDP line. On the PDP-12: "Descendant of the LINC-8; with slight redesign, and different livery, officially followed by, and marketed as, the 'Lab-8'."

http://www.livingcomputermuseum.org