Memory cards are a type of portable flash storage device that are commonly used in portable electronic devices such as digital cameras, some mobile phones and various handheld devices.
These MicroSD cards are segregated by their bus speed - either High Speed or Ultra High Speed (UHS) - this defines the maximum throughput speed of the card; UHS I or U1 - 104MB/s; UHS II or U2 - 312MB/s; and UHS III or U3 - 624MB/s.
They are then broken down into size groups - MicroSDHC (High Capacity up to 32GB ), MicroSDXC (Extended capacity up to 512GB) and are denoted with ‘speed class’ or ‘video class’ ratings of C10 or V10 (up to 10MB/s), V30 (up to 30MB/s), V60 (up to 60MB/s) and V90 (up to 90MB/s), which define their minimum sequential write speeds for higher performance cards.