Detect And Zero Rightmost One (DZRMO)– the title comes from an instruction in the assembly programming language of the 1970s era Western Electric Electronic Translation System (ETS), the heart of which was the Stored Program Control (SPC) No. lA – an electronic control processing system, in other words a special purpose computer. It was the room sized, 40-bit computer that operated the 4A/ETS Crossbar Toll Switching System. DZRMO was an elegant single instruction, scanning an argument in a register for ones, from right to left and for each one detected it would call a subroutine from a list, pointed to by another register, indexed by the position number of the detected one, continuing until all ones in the register were processed.
The memory used by the ETS was the unique Piggyback Twistor Memory. I am not aware of it ever being used in any other computing device. An explanation of this unique memory starts at page 14, paragraph 2.56 of Bell System Practice (BSP) 032-182-101.
Below, is a photo of the ETS console in the Smyrna, Georgia 4A/ETS office, where I worked during the early 1970s.
4A/ETS Console
If you want to know about the 4A Toll switch, the article at THIS-LINK has a good synopsis.
A photograph of the “console” of an #5 ETS is at THIS-LINK. It is similar in appearance to the 4A/ETS.
Some 1972 photos at AT&T’s Atlanta NW (Smyrna, GA) 4A Toll Switch are below.
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- ETS Console TTY
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- In front of ETS
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- Maintenance Center
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- co-workers
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- 17C Test Board
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- 4A Team Greensboro 4A
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- Greensboro ETS Console
Edward Comer
Detect And Zero Rightmost One 