All ABout SD Cards
Secure Digital cards, or SD cards, were developed by the SD Card Association (SDA) for use in portable devices and first launched in 1999 by Panasonic, Toshiba and SanDisk. The design was an evolution of previous storage cards, such as SmartMedia or MultiMedia Card, and offered faster write speeds and more storage than other options available at the time. They've become the standard removable storage for all kinds of portable devices we use every day, but the subtle differences in size and format can be confusing. We'll breakdown the basics of SD cards below so you can choose the right card for your application

Standard vs Mini vs Micro


Standard SD cards are the original design, and the largest form factor of the cards and mostly used in larger portable devices such as D-SLR or video cameras. They're robust and you're much less likely to lose them, but the size made them unsuitable for modern devices where space is at a premium. They measure 32 x 24 x 2.1 mm and have 9 pins.

SD Card


MicroSD cards are the smallest form factor cards, and were designed due to SD cards being too large for mobile phones. Today, MicroSD are the most common type of SD card, used in most smartphones/tablets and almost all of our covert cameras. They measure 15 x 11 x 1 mm and have 8 pins.

Micro SD


MiniSD cards were designed before MicroSD cards for much the same reason. They are smaller than Standard SD cards, but are quite uncommon today, as most electronics use the smaller MicroSD standard. They measure 21.5 x 20 x 1.4 mm and have 11 pins

Mini SD

Write Speeds

SD Cards have different write speeds; higher demanding processes like recording full HD video requires a faster write speed. Write speed simply refers to the speed the card will allow data to be written and saved onto it. Obviously lower demanding processes, like storing and accessing documents can get away with using a slower card, but cost of a high-speed Class 10 card isn’t much more than lower speed cards so it may be worth getting a high-speed card no matter what your application. The write-speed listed on a card is the minimum speed the manufacturer can guarantee, so the real-world speed may be higher.

MARK Minimum Write Speed Application
30MB/s 4K Video Recording
10MB/s Full HD (1080p) Video Recording
Class 10 10MB/s Full HD (1080p) Video Recording
Class 6 6MB/s HD (720) Video Recording
Class 4 4MB/s HD (720) Video Recording
Class 2 2MB/s Photos

Card Capacity Standards

To make things more confusing there are three standards for capacity:

SD standard - Up to 2GB SD memory

SDHC standard - Over 2GB-32GB

SDXC standard - Over 32GB-2TB

SD standard was the original capacity standard, but as demand for higher capacity grew the SDHC standard was introduced. SDHC is the most common standard you’ll see today, the original standard is quite rare now. SDXC is the newest capacity standard, and if you’re considering purchasing a SDXC card you’ll need to check if your device is compatible with the SDXC standard. As a newer standard, a lot of old devices won’t work with SDXC cards.

Speed Bus

One final thing to mention is that some newer SD cards have extra pins to allow much after write speeds. These newer cards use UHS-II (Ultra High Speed II)

UHS-II cards also use a different speed class, using the icons and to show minimum write speeds as 30MB/s and 10MB/s respectively.

Devices need to support the UHS-II class in order to use the extra pins and gain the boost in read/write speed, but if your device doesn’t support UHS-II the card will still work

So, that’s the basics of SD cards. You can find a lot more information at, or we can answer your questions if you call us on 01949 836 990 or leave a comment below.

If you’re looking to purchase an SD card, be sure to check our range.



Posted in News By

Joe Marshall