Introduction⌗

Secure Digital are a memory card type that are typically used in cameras and mobile devices. They are common because of their small size and capability to store information up to a certain size. Initially, the available sizes for the cards were 4,8,16,32,64,128,256 512MB and 1GB, 2GB only. However, demand for bigger size grew and there was a need to expand the sizes past 2GB.

SD

Secure Digital High Capacity (SDHC)⌗

SDHC was created to meet the high demand for High Definition videos and images used in many SD-enabled devices.

It is the same size and shape as the SD cards but it was created to meet the new specification standards version 2.0. An SD card that is above 4GB and below 32GB is categorized as an SDHC.

SDHC

The Secure Digital Card Association (SDA) lay down a speed class rating for the standardisation of data transfer speeds that is compulsory for SDHC:

  • CLASS 2 - a guaranteed minimum write speed of 2MB/s or higher*
  • CLASS 4 - a guaranteed minimum write speed of 4MB/s or higher*
  • CLASS 6 - a guaranteed minimum write speed of 6MB/s or higher*
  • CLASS 10 - a guaranteed minimum write speed of 10MB/s or higher*
  • The minimum speed capability depends on the manufacturer of the host device and model.

If you have a class 2 device, you should not use a class 4 and above SDHC card as it will slow down perfomance of the device.

SDHC are not backward compatible with the standard SD devices. Standard SD cards will not work in SDHC devices as they will be of slower read and write speeds.

Secure Digital eXtended Capacity Card (SDXC)⌗

SDXC is the latest type of memory card released in 2010 which meets the demands of FULL HD recording in terms of capacity and speed. The SDXC card has the same dimensions of a SD and SDHC card, but is ONLY compatible with SDXC devices.

SDXC

SDXC cards are above 32GB with speeds upto 104MB/s and have a roadmap to 2TB with speed up to 300MB/s.

SDXC uses the exFAT file system to handle large data volumes and files sizes over 4GB. A microSDXC version is now also available.

Secure Digital Ultra Capacity (SDUC)⌗

SDUC1 format, described in the SD 7.0 specification, and announced in June 2018, supports cards up to 128 TB and offers speeds up to 985 MB/s, regardless of form factor, either micro or full size, or interface type including UHS-I, UHS-II, UHS-III or SD Express. The SD Express interface can also be used with SDHC and SDXC cards.

SDUC

Conclusion⌗

When getting and SD card, it’s important to know which type of SD card your device accepts. This will prevent you from getting a higher class card that is not compatible with a lower class device.

  1. https://en.wikipedia.org/wiki/SD_card ↩︎