If I remember correctly, you used to be able to actually take the magnetic material out of the sleeve and it would run in the drive.

You just reminded me of a curiosity that were the DVD-RAM discs - they came in plastic cases with a sliding window(exactly like a floppy) and there were special drives that accepted them in the case. However you could remove it from the case and most regular DVD drives would read and write them without any issues.

https://en.m.wikipedia.org/wiki/DVD-RAM

My first 1x burner used a cartridge and slot.

Some good coverage on DVD-RAM & caddys from technology connections: https://www.youtube.com/watch?v=ecH3OU0R4ls [DVD-RAM: The Disc that Behaved like a Flash Drive]

https://www.youtube.com/watch?v=jxt5A0KJ9nw [Early CD-ROM Drives: Why Did They Require a Caddy?]

The early Apple CDROM drives also took a caddy that you put your disk into.

The proposed Nintendo/Sony CD-ROM was also caddy based.

I just remembered that UMD discs for the PSP came in a plastic case(which stupidly didn't include a sliding window, leading to the discs getting scratched even though they were in the case).

You can technically still do this with 3.5" disks, it's just a invitation for horrible mechanical problems when (not if) the disk touches something it shouldn't or unseats from the drive motor. Also you need to manually push various latches and levers that the sleeve would have run into.

I did one day put a 5 1/4 floppy in the small gap between 2 drive bays. Plonk! Oh well, time to get the screwdriver. I heard it happened a lot at the time.

Also on the Mac II, when the blank hiding the second floppy slot used to fall down. I remember a secretary calling in distress after having inserted 20 floppies or so inside the Mac to no effect: they were all piling up inside, behind the floppy 2 slot :)

Thats ok, anyone who has been a bench tech, field tech, especially in the later 90s to early 2000s, has a similar story to this. Ive had people manage to force CDs between two drive bays and wonder why their CD wasnt being detected. Have had people insert credit cards in floppy drives, etc..

[Edit] there used to be a website, similar to bash.org, that people would submit stories like this all the time of stupid shit they were running into as a tech. Dont recall what it was. There was also and admin site, they may have been the same.

http://rinkworks.com/stupid/ ?

One of the older ones was the daily wtf, still around but not nearly as good as it used to be. There's a subreddit /r/talesfromtechsupport that has become my go-to for that now.

Not on the standard 3.5" but I believe I've seen some (very old very obscure) solutions like that.