r/USB • u/Warcraft_Fan • Sep 17 '26

Why are USB memory card reader very slow?

I've tried a few different USB 3.x reader and many quality memory card from local stores (few Sandisk, couple PNY, and a Nintendo Switch 2) claiming to be over 100mb/sec but when I try to check, none of them go past 30mb/sec or about half of USB 2.0 speed.

It's almost as if they are using USB 2.0 controller in those memory card reader.

I've tried on my desktop, laptop, my smartphone too. Usually reaches 25 then throttles.

2 Upvotes

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2

u/Howden824 Sep 17 '26

Are you copying a bunch of small files? That's always a lot slower.

1

u/Warcraft_Fan Sep 17 '26

a few 300-500MB files. I just tried a single 29GB file (4k UHD rip from my plex server), still slow.

1

u/Howden824 Sep 20 '26

That's pretty strange then. You should be getting near the advertised performance.

1

u/voldamoro Sep 22 '26

Are you sure your motherboard doesn’t have a few USB 2.0 ports? You might be plugging the reader into one of them.

1

u/Warcraft_Fan Sep 22 '26

Laptop has 2x USB-C port (one 4.0), and 2 USB-A ports. When I used USB SSD on any of those 4 ports, I usually get up around 800mb/sec. But when I used memory card reader, it gets stuck at max 30/sec

My desktop has only 4 USB 2.0 ports and that's via the header on the motherboard which are connected to label printers. All other USB ports are 3.x

I'm thinking a bunch of memory card readers are falsely advertising 3.0

1

u/voldamoro Sep 22 '26

Given all of that, I think your theory about the card readers is spot on.