Product Guide

Buying guide

There are some important factors to consider when buying SD cards this guide will help you make your selection. most cards of the correct size will work in your device but there are subtle differences in performance.

Lets start with the most important factor, Size!

  • Standard SD cards: SD (SDSC), SDHC, SDXC — 32 x 24 x 2.1-1.4mm
  • miniSD cards: miniSD, miniSDHC — 21.5 x 20 x 1.4mm
  • microSD cards: microSD, microSDHC, microSDXC, microSDUC — 15 x 11 x 1m

Definitions  of SD cards can be confusing but it is important to understand that the primary purpose of most of these definitions are to set a standard for manufacturers to follow when making these SD cards so that devices can be produced knowing that compatibility won’t be an issue.

SD definitions refer mainly to capacity and to some degree the speeds due to different revisions of each capacity when the technology improves. These are the typical definitions you might see as defined by the Standard Digital or the SD foundation:

*note that miniSD and microSD follow the same guidlines

  • SDSC – (SD Standard Capacity) SD cards upto 2GB in capacity
  • SDHC – (SD High Capacity) SD cards between 2GB and 32GB
  • SDXC – (SD Extended Capacity) SD cards upto 2TiB
  • SDUC – (SD Ultra Capacity) SD cards upto 128TiB
  • SDIO – (SD Input/Output) A rare SD card used for specific interfaces

These also give an idea to the default format of the cards:

  • SDSC – FAT16
  • SDHC – FAT32
  • SDXC – FAT32/exFAT
  • SDUC – exFAT

Now to some more relevant information speed! SD card speed is related to its sequential read or write speeds. Writing is typically more intensive on the cards and also slower. Write intensive devices such as security cameras would benefit from using high endurance SD cards.

Speed is directly related to the bus in the cards and, think of a bus as a motorway with a number of lanes transferring data. newer and higher speed cards typically have more lanes to transfer data reflected by having more physical connections on the card.

  • Default speed – SD cards will read and write at speeds of 12.5MB/s.
  • High speed – SD cards will read and write at speeds of 25MB/s.
  • UHS – (Ultra High Speed) which seperates into 3 different classes as of 2020.
  • UHS-I – SD cards will read and write at speeds of 50MB/s with a subclass UHS104 supporting upto 104MB/s transfer speeds.
  • UHS-II – SD cards will read and write upto 156MB/s or 312MB/s depending on interface (full or half duplex).
  • UHS-III – SD cards will read and write upto 312MB/s or 624MB/s depending on bus.
  • SD Express – SD cards will read and write upto 985MB/s or higher depending again on version.

The C, U and V symbols seen on many SD cards also refer to write speed (see table below) and typically relate to some of the points already covered. It is important to note that SD card read/write speeds can vary and depend on many different factors such as manufacturer, device, interface and use. 

*Information sourced from wikipedia

SD Card specifications chart
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