SD card speed on different controllers - read went up but write went down

ET

Senior member
Oct 12, 1999
521
33
91
I got a new 32GB microSD specced at 40MB/s read, and used CrystalDiskMark on a couple of laptops to check the speed. On a couple of laptops it showed 19MB/s read, 13MB/s write. On a MacBook Pro (2011) it shows 43MB/s read, 9MB/s write. (All laptops are using Windows 7 x64.)

I've read about old controllers using USB 2 and therefore being limited to around 20MB/s, and I guess the MacBook Pro is using a newer one, but why would write speed be slower than on the other laptops?

Anyone has an idea?