I was just listening to Lets Push Things Forward by The Streets (which has the temerity to be released 20 years ago 
)
And I realize it contains the line "You won’t find us on Alta Vista. Cult classic, not best seller. "
Referencing the “also ran” search engine that was a competitor to Yahoo and precursor to (and swiftly surpassed by) Google in the late 90s/early 00s.
What glaringly dated (and slightly obscure) tech references are there in song?
I heard you on my wireless back in '52
Not really obscure though. I mean people generally know what a song that refers to wireless radio, CDs, telegrams, email etc. is getting at, even if they are to young to have used any of those things.
Most of Weird Al’s All About The Pentiums still holds up - 100 Gigs of RAM, 40" Flat screen etc are still good.
But “Installed a T1 line in my house” is no longer the flex it once was…
Maybe it’s not a dated tech reference, maybe the band is just from Pawnee, Indiana.
(start at 8:42)
That would be a bigger bombshell revelation about The Streets than the reveal of who they wrote “When You Wasn’t Famous” about 
MF Doom / Who Do You Think I Am?
So socialize my bio so I dip dip dive
Memorize like I-omega zip drive
Probably plenty of us here know what a Zip drive is, but I doubt many Millennials do.
Oooh, serendipitous! That very song actually contains another, much more dated “tech reference”: namely, the phrase “watch the birdie”, which originated with the then-novel technology of photography.
ETA: I also nominate Donna Summer’s 1979 song “Dim All the Lights” for its line “Turn up the old Victrola”, which IIRC even at the time was a fairly old-fashioned term for a record player. Actually, “Victrola” seems to be mentioned in quite a few songs even as recently as the 2010s. Hmmm.
Furthermore, I’d like to know if the OP is seeking just song references to technology which happens to be very dated/obscure right now, even if it was cutting-edge at the time the song was written? Or is the goal to find the tech reference that was the most obscure and dated even at time of writing, i.e., the longest chronological gap between technology development and its mention in song?
Because if it’s the former, I got 19th-century music-hall and similar songs that will knock out any competition from their computer-era counterparts. An 1892 paean to the medical device known as an “electric belt”, anyone?
If it’s the latter, I was thinking that the recent “Victrola” references (e.g., in Charlie Worsham’s 2017 “Cut Your Groove”) would be a sure winner. But now I’m doubtful because I’m not sure how dated or obsolete the Victrola really is. It certainly dates back to the early 20th century, but when (if ever?) did people actually stop using devices unironically called a “Victrola”?
The song Stereophoic sound by Cole Porter has a bunch of obscure film tech references.
The customers don’t like to see the groom embrace the bride,
Unless her lips are scarlet and her mouth is 5 feet wide,
In: glorious Technicolor, breathtaking Cinemascope or Cinerama,
VistaVision or Superscope or Todd-AO or
Stereophonic sound or stereophonic sound.
When I was young in the 70s, that phrase was still used by many photographers even though it was long obsolete, and they were not holding anything up next to the camera. For years until I learned otherwise, I thought the “birdie” was that little flicker I could see inside the lens when the shutter was open briefly, somewhat akin to a cuckoo clock.
For the sake of pedantry, (and what else is the Dope for) how about any number of folk or modern songs about with lyrics of picks, shovels and steel making? Or indeed older technologies.
Yeahbut, people do still use picks, shovels and steel. I thought the idea was to find references to technologies that had become decisively obsolete, either by now or by the time when the song referring to them was written.
But I’ll let the OP referee that point.
How about:
Outkast’s “Hey Ya!” calls for listeners to “Shake it like a Polaroid picture”, a reference already dated at the time of the song’s release.
Old 97s “Big Brown Eyes” has the line “I’m calling Time and Temperature just for some company”.
Jay Z’s 2013 single “Tom Ford” references the blogging site Tumblr, which even then was rather obscure. (I had to check, but apparently it still exists.)
“Little Red Light” (a great rocker by Fountains of Wayne) features dated if not obscure tech:
I come back home
But you’re still gone
And I’m still alone
And the little red light’s not blinking
No, no the little red light’s not blinking
No, no the little red light’s not blinking
On my big black plastic Japanese cordless phone
Oh no
I can’t speak for all millennials obviously, but I remember the iOmega commercials airing on TV when I was in high school. In my mind they were the transitional portable storage medium that existed between 3.5" floppy disks (which I also used in high school) and USB sticks.
I think I would still consider it an obscure tech reference though.
This whole song (Operator by Jim Croce in 1972) is about pretty dated tech even when it came out. As a teen I’d certainly heard of such tech & seen it in movies, but had never encountered it in real life:
Heck, even the mention of “matchbook” has gotten pretty dated today. A mere 50 (!!?!?!11!) years later.