Editing SD card (section)

=== Real-world performance ===
Speed Class ratings guarantee minimum write performance but do not fully describe real-world speed, which can vary based on factors such as [[file fragmentation]], [[write amplification]] due to flash memory management, controller retry operations for soft error correction and sequential vs. random write patterns.

In some cases, cards of the same speed class may perform very differently. For instance, random small-file write speeds can be significantly lower than sequential performance. A 2012 study found some Class 2 cards outperformed Class 10 cards in random writes.<ref name="necstudy" /> Another test in 2014 reported a 300-fold difference in small-write performance across cards, with a Class 4 card outperforming higher-rated cards in certain use cases.<ref name="Gough2014" />