SF's Market Street Subway Is Running on Reagan-Era Technology:

"Our train control system in the Market Street subway is loaded off of five-and-a-quarter inch floppy drives," SFMTA director Jeffrey Tumlin told KQED's Priya David Clemens this week. "We have to employ programmers who are experts in the programming languages of the nineties in order to keep running our current system. So we have a technical debt that stretches back many decades."

Ah yes, the withered programmers from the Nineteen-Hundreds. I'm glad they included these historical fun facts about floppy disks!

For those who've never had to use one -- and keep it far away from any magnets -- floppy disks are still used as the "save" icon on computers worldwide, but they've been obsolete for 30 years or more. Originally a full eight inches across when introduced in the 1970s, floppies later shrunk to five-and-one-quarter inches, and, eventually, a mere three. Early generations were indeed bendable, although the final generation was made of a harder, thicker plastic, with no flop at all. Eventually, CD-ROM technology superseded them before becoming nearly extinct, too.

Here's an article from 2015 about some upgrades, but this sounds like an even older, pre-floppy system:

Muni train control system gets biggest upgrade since the '90s:

In a dank walkway tucked away inside the Van Ness Avenue Muni station is the mainframe that controls Muni trains underground.

Relay racks extend down a cramped hallway nearly 15 feet deep, where dozens of 4-inch copper filaments clatter up and down like teeth. The speedy "click, clack" sound signifies a smooth running Muni light rail automatic control system [...] The clapping beat signifies the proper alignment of the railway's 83 axle (controls) and numerous other track switches. [...]

When this happens, or a track switch is damaged, a green relay cable running the length of the underground track is tripped. This signals the maintenance crew, which then checks each ticking copper relay for those with an off beat, or ones that have stopped altogether. [...]

"Last year, we had water up to here" Haley said, gesturing with his hand to his waist. The relay system is under a city drain, he said. A yellow tarp is strung at the roof of the relay room, while sandbags, a bucket and more tarps are tucked away in the corners. [...]

"These things are hard to replace," Kelly said. "You can't just go to Relays R Us." [...]

The crew that maintains and inspects the relays every night said it is hopeful for the new system -- but it also respects the old one. "I trust it to run another 20 years," said Hoa Huynh, a 20-year maintenance crew member. But, he said, "It's slow. Very slow."

I love the idea that part of the diagnostic process is to stand in this room and listen to it -- "that's not how the tunnel song is supposed to go." An interface that draws big red boxes using a supercomputer is not necessarily easier or more expressive than one that communicates ambiently through the system's inherent musicality.

Previously, previously, previously, previously, previously, previously, previously.