One thing that is almost universally true (at least as of 2019) is that the most common system boot device is a microSD card. SD cards in general have performance characteristics that pale in comparison to faster devices, like NVMe SSDs, eMMC, and XQD or CFexpress.
On top of that, the performance metrics used in microSD marketing are usually targeted only at the major market for these tiny memory chips: those who record video and stills on them, and only ever really care about massive file read/write performance.
For general purpose computing—which is what SBCs like the Raspberry Pi do—random I/O performance is much more important. And here is where most of even the most expensive microSD cards fall incredibly short.
Each Friday is PiDay here at Adafruit! Be sure to check out our posts, tutorials and new Raspberry Pi related products. Adafruit has the largest and best selection of Raspberry Pi accessories and all the code & tutorials to get you up and running in no time!
Stop breadboarding and soldering – start making immediately! Adafruit’s Circuit Playground is jam-packed with LEDs, sensors, buttons, alligator clip pads and more. Build projects with Circuit Playground in a few minutes with the drag-and-drop MakeCode programming site, learn computer science using the CS Discoveries class on code.org, jump into CircuitPython to learn Python and hardware together, TinyGO, or even use the Arduino IDE. Circuit Playground Express is the newest and best Circuit Playground board, with support for CircuitPython, MakeCode, and Arduino. It has a powerful processor, 10 NeoPixels, mini speaker, InfraRed receive and transmit, two buttons, a switch, 14 alligator clip pads, and lots of sensors: capacitive touch, IR proximity, temperature, light, motion and sound. A whole wide world of electronics and coding is waiting for you, and it fits in the palm of your hand.