UHS is a new ultra high speed bus (data transfer connection) for SD memory cards. There are two versions: UHS-I and a more advanced UHS-II type. This refers to the physical construction of the card and does not directly indicate its speed. There are speed standards for UHS cards: UHS 1 guarantees a minimum speed of 10MB/s, which is suitable for full HD video recording, and UHS 3 guarantees a minimum transfer speed of 30MB/s, which is what you’d need for 4K video.

SD, SDHC, SDXC cards

These are all the same size but there are important differences. Older cameras may only be able to use SD cards, but more recent ones will be able to use SDHC cards too, but may not be able to use the latest SDXC format. Check your camera’s manual before buying these.

Memory card speed

Memory card makers quote the card’s maximum read/write speed in MB/sec, but it’s also important to know the minimum sustained speed for video recording. This is quoted using Class ratings (SD cards). Typically, you need Class 10 for 4K video as a minimum.

Memory card capacity

This is measured in gigabytes (GB), and the larger the memory capacity the more photos and video clips you can store. It’s hard to give precise advice since cameras and user needs vary so much, but 16GB is a good starting point if you shoot RAW files as well as JPEGs, and consider 64GB-256GB if you want to shoot video, especially 4K.

Memory cards

Removable storage media used to store digital images in the camera. They come in different types (SD, Compact Flash, XQD, CFast), different capacities and speeds.

Format (memory card)

Completely wiping a memory card so that you’re starting again with a clean slate, so to speak. It’s not essential if you only ever use one camera, but if you use the same card in more than one it will clear up unwanted files and folders left behind by other cameras.


A brand of memory card that includes Wi-Fi capability so that you can transfer photos wirelessly to a smartphone, tablet or computer. More and more cameras are coming out with Wi-Fi built in now, though, so these provide the same functionality as Eye-Fi cards.

Compact Flash

An older, larger memory card type still used in many professional cameras. It’s around twice the size of the more recent SD card format and thicker too. Compact Flash memory card capacity is measured in the same way in GB (Gigabytes) but speed standards may vary, especially for video use. Professional CF cards offer the same speeds and capacities as pro SD cards.

Card reader

Device used for easily transferring photos from a memory card to a computer. Card readers plug into a computer’s USB port and have slots for inserting memory cards. When the card is inserted it appears on the computer’s desktop as an external disk drive. It’s then an easy matter to copy photos across to the computer. Many computers how have card readers built in.