The Names

SD, SDHC and SDXC all physically look the same, therefore they’ll all fit in a regular SD card slot. The only thing you may need to check (especially for older devices) is the max capicity your device can take. Micro SD Cards are similiar, but smaller.

• SD cards is used in most modern digital cameras and nearly all laptops will come equipped with an SD card reader slot.
• SDHC = Secure Digital High Capacity This was initially introduced to cover SD cards with a capacity above 2GB and below 32GB.
• SDXC = Secure Digital eXtra Capacity These go far beyond 32GB in size.

Speed Classes

Many SD card manufacturers will also list a specific speed alongside the Class rating. This means a card can be Class 10 but also be listed as ‘up to 80MB/s’. The wording is important, as that’s the best you can expect but not necessarily what you’ll always achieve. On any type of SD card, the Class rating is denoted by a number inside of a C symbol. - FOR ALL TYPES OF SPEED CLASSES THE BIGGER NUMBER IS ALWAYS FASTER.

• Class 2 (minimum write speed of 2MB/s)
• Class 4 (minimum write speed of 4MB/s)
• Class 6 (minimum write speed of 6MB/s)
• Class 10 (minimum write speed of 10MB/s)

UHS Speed Classes

UHS came about due to 4K-capable video devices needing faster write speeds. The UHS Speed Class is denoted by either a 1 or 3 inside of a bucket U symbol. As a rule of thumb, 4K-capable camcorders will usually require at least a U3 rated SD card.

• UHS Speed Class 1 (minimum 10MB/s write speed)
• UHS Speed Class 3 (supports at least 30MB/s write speed)

UHS Bus Speed Classes

Note that unlike the UHS Speed Class, these are not sustained speeds.

• UHS-I (maximum read speed of 104MB/s)
• UHS-II (maximum read speed of 312MB/s)