What are all the symbols on SD cards?

Inspiration

I need to buy an SD card because my Flipper Zero arrives in a few days. I want to know more about those symbols on SD cards.

Findings

• The bus interface determines the maximum bus speed at which a memory card can transfer data. Nearly all SD cards today have UHS-I or UHS-II bus interfaces. These are marked on the card with roman numerals
• Speed class ratings define the minimum sequential write speed of the memory card. This is important for shooting video because a memory card must maintain a certain continuous write speed to avoid frame drops and errors during recording
• Speed classes
  • Speed Class
    • Marked by a number inside the letter C
    • The number indicates a minimum sequential write speed. So a C10 rating would sustain a write speed of 10 MB/s
    • There are five ratings in this speed class: C2, C4, C6, C8 and C10
  • UHS Speed Class
    • Marked by a number inside the letter U
    • This number must be multiplied by 10 to get the minimum sequential write speed. So a U3 would sustain a write speed of 30 MB/s
    • There are only two ratings in this class: UHS Speed Class 1 (U1) and (U3)
  • Video Speed Class
    • Marked by the letter V followed by a number
    • The number is the minimum sequential write speed in MB/s
    • There are five ratings in this speed class: V6, V10, V30, V60 and V90

Etymology

Follow-up questions

What is a bus interface?

• A Reddit thread had this answer
  • A bus moves data around. An interface is the entry and exit to the bus.
• An interface is the point of contact between two surfaces
• A bus is a communication system that transfers data between components inside a computer or between computers. It encompasses both hardware and software, including communication protocols. At its core, a bus is a shared physical pathway, typically composed of wires, traces on a circuit board, or busbars, that allows multiple devices to communicate

What is UHS-I or UHS-II?

• According to ProGrade Digital, UHS is the specification that deals with how fast data can move in and out of the card via the communication bus. Note that this really is about the speed of the bus and not the speed of anything else in the card. UHS-II improved on UHS-I by adding more pins to the connector.

• There are SD Express card that use the PCIe bus interfaces and NVM instead of the SD bus interface

Does the speed class matter for photography?

• It does if you’re shooting high-resolution images or recording a lot of video.

When was the Video Speed Class created?

• My mom looked into this for her photography a while ago and took away that a C10 was the best at the time
• It sounds like the Video Speed Class came out later and surpassed C10.
• 2016, but that’s when it was “formulated”. It doesn’t mean it reached mass market implementation on SD cards, yet

What does A1 and A2 mean?

• They’re the raitings for the application performance class of the card. It measures how well an DS card can run mobile applications