wil bierbaumFeb 19
Tom Lyon ✅

Before transistors, relays were widely used in telephony switches. They were much slower, but much more reliable than vacuum tubes.

This 1951 booklet, "NO. 5 CROSSBAR" from Bell Labs describes the bad-ass mainframe of relays. Lots of photos and diagrams.

https://drive.google.com/drive/folders/1UBnLJIzYjpGu1401I6F3lDa9fWiXSBu5?usp=sharing

Feb 19 at 1:32amWeb
Show threadSnoopJFeb 19
@aka_pugs ooooh, thank you for sharing
Show threadKernel Bob Feb 19

@aka_pugs Did you spend any time at TMRC? In the 1970s and probably '80s, power to the rails went through five 10x10 crossbars as part of an all-relay power routing . It was a rite of passage to understand how the all-relay system worked (one that I never completed).

Edit: surplus/recycled Western Electric crossbars.

Show threadTom Lyon ✅Feb 19
@kbob No, I only know of it through lore, incl. Firesign Theater.
Show threadLauren WeinsteinFeb 19
@aka_pugs #5 Xbar is my favorite AT&T switching system, with the proviso that AT&T SXS had its, uh, advantages as well.
Show threadThe Orange ThemeFeb 19
@aka_pugs That diagram is sublime. 🥵