SD cards are present in a large number of gadgets such as cameras, smartphones, tablets, GPS, Blu-ray players, video game consoles and many other electronic devices. As we generate more and more content and media, the need for storage keeps growing. SD cards have become one of the most popular storage equipment thanks to their size and capacity. They are also very easy to use (plug- and-play), and can usually be purchased at an affordable price.

The SD Association, consisting of members like Toshiba, Panasonic, Canon, Tuxera… was established in 1999 and it is responsible for maintaining the standards related to this type of storage. Since the first SD standard, the so-called SD Specification 1.0/1.1, SD cards have undergone several developments. In this post we will explain you the most relevant concepts related to SD cards.

Types of SD cards: standards and physical size

The SD specifications developed for the past 15 years have led us to three different standards: SD, SDHC, SDXC. See the table below for a summary:


It is however more common to distinguish between SD cards according to their physical dimensions: SD, miniSD, microSD. SD cards are the largest and have a “cut corner”  design. MiniSD cards are lighter and smaller than SD cards, but this size is not common today since the launch of microSD cards, the smallest of all.


To put it all together in a simpler way, check out this table from the SD Association:


Speed class rating

The speed class rating was introduced by the SD Association as a way to quickly provide information about the minimum writing performance of the card, in order to help consumers decide what card to purchase.


It is important to note that the speed class rating shows the minimum speed of the card, not its actual speed. Just because two cards have the same class it does not mean that both cards will perform equally. Manufacturers usually go well above those minimum requirements and offer much higher speeds. In addition, the host device also plays its part. A card might support writing at 100 MB/s, but the device might not be capable of sending data as fast as it can be written. The compatibility specs offered by the device should always be checked.

To recap, not all SD cards are the same: size, capacity, speed and intended use are the determining factors when comparing SD cards. SD cards are ideal for getting extra storage in your smartphone and tablet; and virtually the only choice for camera users. Did you know that Tuxera exFAT is the main driver behind SDXC adoption? Take a look at our file system products and find out more about our technology.