Secure Digital Cards Explained

The Numbers & Symbols on Your Card Explained

Take a look at your DSLR, mirrorless camera or camcorder and the chances are it supports Secure Digital (SD) memory cards. SD has become today’s standard memory card format as it is widely accepted in both consumer and professional-grade cameras. But despite how commonly used it is among photographers and videographers, there are many who do not realize that not every SD card is the same. Here, we’ve broken down the common terms and symbols found on a SD card in order to help you understand the difference between cards, as well as which cards are best for certain cameras.
TERMS & SYMBOLS:
  • SD / SDHC / SDXC
  • UHS-I vs UHS-II
  • MAXIMUM READ SPEED
  • MAXIMUM WRITE SPEED
  • SPEED CLASS
SD / SDHC / SDXC:
The terms “SD”, “SDHC” and “SDXC” specify the capacity range of the memory card. “SD” cards can go up to 2GB, while “SDHC” ranges from 4GB to 32GB, and 64GB to 2TB for “SDXC”.
UHS-I vs UHS-II:
The UHS-I bus interface allows for transfer speeds up to 104 MB/s, while UHS-II boasts significantly higher speeds up to 312 MB/s. This is due to UHS-II cards being designed with two rows of pins, rather than one like UHS-I, which allow for two lanes of data transfer.
MAXIMUM READ SPEED:
The fastest speed that data can be transferred from the card to a computer. The higher the read speed, the less wait time and sooner post-production can begin. High read speed is ideal for photographers and videographers who need to quickly unload large amounts of data and get back to shooting.
MAXIMUM WRITE SPEED:
The fastest speed that data can be written to the card. The higher the write speed, the more you can capture in a certain amount of time. High write speed is ideal for photographers and videographers who are shooting in demanding capture modes, such as high-resolution video and RAW burst photography.
SPEED CLASS:
Speed Class (Class 2 to 10), UHS Speed Class (U1 or U3) and Video Speed Class (V6 to V90) indicate an SD card’s minimum sustained write speed (e.g. 10MB/s for Class 10 | 30MB/s for U3 | 90MB/s for V90)
CLASS 10 / U1 / V10:  SD cards rated Class 10 / U1 / V10 are ideal for still photography and Full HD 1080p video recording @ 30fps.
U3 / V30:  SD cards rated U3 / V30 can handle flawless 4K video recording @ 30fps and RAW burst photography.
V60 & V90:  SD cards rated V60 and above are optimized for 6K & 8K video recording at high frame rates & bitrates, as well as simultaneous multi-file recording (e.g. RAW + JPEG, multiple video streams created by 360º cameras, video + still + GPS data, time-lapses, etc.)