[jack12]

My understanding is that A2 cards are generally slower than A1 cards IF you don't have host-side support for managing the volatile-RAM caching that A2 requires.

So if the Pi 4 only allows you to run in A1 mode anyway, you're better off buying the A1 card and both saving money and getting a faster card. I don't know if that lack of support is true of the Pi 4, but it does seem to be true of most other SBCs according to https://github.com/ThomasKaiser/Knowledge/blob/master/articl...

[meatmanek]

Ah, interesting, I did not realize there was a difference in protocol. I thought A1/A2 were just spec requirements.

I wonder if A2 support is something that could be added in newer kernels, or whether it requires hardware support.