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I'm hoping to do a series of articles / threads about how the PDP-12 works, by diving into its instruction set and other low-level behaviors. Here's the first one of these threads! 🧵 #pdp12 #umdpdp12 #RetroComputing 
The PDP-12 is a combination of the LINC and the PDP-8 -- both 12-bit machines. The practice was to describe memory using four octal (3-bit) values (rather than, say, 3 hexadecimal values). So, 111111111111b is "7777" (not 0xFFF) and 101010101010b is "5252" (not 0xAAA).
The PDP-12 runs in either LINC mode or PDP-8 mode at any given time, but you can arbitrarily switch between modes (and instruction sets) at any time, using ops PDP (0002) in LINC and LINC (6141) in 8-mode. Some hardware only works in LINC mode, so this is quite common.
