The Switch 2’s additional power opens the door to more complex games that could lag even more noticeably, especially if they’re ported from consoles that expect more than 50 times the storage bandwidth (Sony requires an SSD with read speeds of at least 5,500MB/s for the PlayStation 5).
And that’s where SD Express comes in. These cards are connected to the same PCI Express/NVMe interface that internal SSDs use in modern PCs and the other game consoles, theoretically giving your SD card access to the same bandwidth as internal storage.
Now, you won’t actually get performance as fast as an internal SSD using this interface. The speed varies a lot based on the PCI Express version your gadget is using (3.0 or 4.0) and how many “lanes” of bandwidth it’s allowed to use (these are, in short, the connections between a device’s CPU and external accessories like SSDs, Wi-Fi adapters, or dedicated GPUs, and all CPUs and SoCs have a limited number of them to hand out). Depending on these factors, microSD Express can deliver anywhere between 985MB/s and 3940MB/s of theoretical bandwidth.
MicroSD cards will also be slowed down because there are fewer physical flash memory chips to write to at a time, a process called “interleaving” that is responsible for much of an SSD’s speed. This SanDisk microSD Express card, one of the only ones actually available at retail right now, lists its top speeds as 880MB/s for reads and 650MB/s for writes.
But even at its worst, this is several times the amount of bandwidth available to whatever UHS-I microSD card is inserted into your current Switch. Express cards won’t make an SD card feel as fast as internal storage, but it will help the microSD card keep pace a bit.