eMMC has several advantages over microSD cards.

For example, the microSD slot only has 4 data lines. eMMC isn't constrained to the microSD slot, so they can have 8 data lines.

The Raspberry Pi 4 Compute Module has onboard eMMC. Jeff Geerling tests a lot of SD cards on the Raspberry Pi, but he found the CM4's eMMC is faster than any SD card he's ever tested: https://www.jeffgeerling.com/blog/2020/raspberry-pi-compute-...

Then do we have "eMMC" equivalent quality SD cards that lasts just as long?

Yes, they're marketed as "industrial grade MicroSD cards" and are available via electronics component distributors like Digi-Key.

e.g. https://www.digikey.com/en/products/detail/swissbit/SFSD032G...

That costs more than the rpi itself!

is there anything marketed as "industrial grade X" that costs less than a rpi?

Drop the e and you have an MMC card.

Why is that more useful than a removable SD card?

I think the comment was a bit tongue-in-cheek. The underlying storage tech between is the same, but eMMCs have a controller that handles the actual layout of the data. In a removable SD card setup, this is handled by the CPU, which of course has many other things to worry about. Having its own controller makes eMMCs more reliable.

"eMMCs have a controller that handles the actual layout of the data"

Maybe there is some part that eMMCs have that SD cards don't, but SD cards absolutely do have a controller that does layout (wear levelling). It doesn't do the filesystem layer, but IIRC eMMC's don't either.

AFAIK the only reason SDs are less reliable, is because they're cheap and the socket can be loose, causing corruption during a write (or wear level). It would be interesting if you know of something logically different that also makes them less reliable.

SD cards used to be optimized for usage patterns typical in a video or foto camera (big files, written at once). eMMCs are better adapted to serve as a traditional filesystems for e.g. phones.

Don't find source now though, so maybe I'm completely wrong.

That's true, I remember reading that somewhere too.

The main advantage of eMMCs in reliability is that you can't buy a RPi with a eMMC for camera use soldered on. You can have this same advantage by buying the right kind of SD cards (embdedded/industrial ones, or on a budget, overkill capacity "surveillance" camera cards that advertise wear leveling).