I ordered an odd but very interesting SR from my favourite NOS shop - Unicorn-Electronics in USA:
Fairchild 3357-2: 4 x 80 Bit Static Shift Register
It’s a PMOS device requiring a XXXXXX minus Vdd (well there will be -12V in the rack) and I have even managed to find a pinout (where ever I put that paper 
.
Here’s me wondrings:
The SR has two sets of inputs - just Input and RECIRCULATE. What is that exactly and how to use? In my wildest thoughts, this kind of SR could have been used in good old CRT terminals holding one line of text (80 characters) on the screen, and using the recirc to refresh the 7 or 8 lines that made up the characters.
The other wondring is simple - what should I do with this one? I had ideas of using it in some kind of random CV generator like the Turing machine or The Mad Monkey or CGS’s Infinite Melody.
I could well imagine to start off with a shorter, 6 step or serial-in-parallell-out SR that fed this one that recirculated back to the first shorter SR … somehow 
From the datasheet at page 3-52 of the 1975 Fairchild MOS/CCD Data Book, the Recirculate input simply selects between the D input and the Q output to feed the shift register.
The first application that comes to my mind is an 80 step, four channel rhythm sequencer, where you can modify each of the four synchronous loops independently.
With the circuit set not to repeat, it could be used as a rhythm delay, potentially with up to four equally spaced repetitions of whatever rhythm is provided at the input (there is only a single common clock for the four shift registers).
The four channels could also be combined, and with the addition of a handful of resistors forming a 4-bit DAC, made into an 80 step “analog” sequencer.
The data book also says that theses things can run fast (up to 2MHz) so in addition to the typical sequencer type applications, you can explore some pulse width modulation like generation of analog voltages (à la 1-bit DAC).
OK, no spectacular ideas, but at least I tried.
You could make a digital noise generator with quite a long period with your shift register and some XOR gates - search for “LFSR”. You could clock it at audio rates for white noise, or step through it like a sequencer.
Or you could use it to drive 10 seven segment displays if you wanted some retro UI…
Cheers
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OH GREAT!!! That picture explains a lot! THANKS!
I’ve got two of these, so I have 8 channels (that also could be combined into 1-bit 640 step SR.
I have one idea that, however, requires some intelligence; a step sequencer where the sequence slowly changes little by little.
I imagine that the “recirculate” input just pipes whatever you give it back through the register. It sounds kind of the way the MTM Turing Machine module works–just makes a repeating loop until you add or subtract something from it.