Look at storage and speed when comparing the capacity of digital camera memory cards. These metrics determine how fast a camera operates and how many images it can store during picture-taking. They also allow photographers to judge performance across different types of memory cards.
The speed of a digital memory card is important in capturing image data to the memory card and transferring it to a mobile phone or personal computer for further processing. The speed rating is printed on the face of every digital memory card, indicating the minimum data transfer rate. As of 2015, cards are classified on a continuum ranging from class 2 for a low-resolution video to class 10 for an HD-quality video.
Storage is expressed in more familiar terms. Similar to personal computer hard drives, cards are categorized according to the number of gigabytes they contain. Larger megabyte cards can store more images, depending on the type of format. For instance, a 32-GB card can hold a maximum of 4,600 pictures taken on a 21-megapixel camera. Conversely, a 4-GB card can hold about 500 images taken by the same camera.
For many people, the final criterion in judging memory cards is cost. Cards with higher speeds and larger memory sizes typically cost more.