How does an SD card work anyhow?

Both microSD and SD cards work generally the same. Each card uses a tiny processor and one or two small NAND flash memory chips to manage the flow of data and instructions. Using these electronic components, the SD card is able to write and read data at dizzying speeds. These speeds can range from 2 megabytes per second to up to 90 MB/s.

MiniSD is another SD format, however it's not as widely used anymore, so it is not including in this guide.
CompactFlash, CFast and XQD memory cards are not covered in this guide.

Above: Inside a 2 GB SD card - two NAND flash chips (top and middle), SD controller chip (bottom)

Data transfer

All SD and microSD cards use small brass contacts on the bottom of the card to send and receive info, via instructions and data. 


SD cards: Typical Use Cases and Dimensions


SDs are larger than microSD cards and measure 1.26 x 0.94 x 0.083 to 0.055 inches or 32 x 24 x 2.1-1.4 mm


Where are they used?

Most SD cards are used in DSLR cameras, video game consoles, home theater devices like Blue-ray players, Internet of Things devices like security cameras, and others. Many other devices that used SD cards in the past such as smartphones, have transitioned over to the smaller microSD format.

dslr camera. source:
DSLR SD card. source:

The locking toggle

SD cards have a mechanism on them that allows them to be "locked" and "unlocked". This toggle enables or disables the ability to write or delete data on the card. 

This feature is useful when you want to prevent the files from being changed in any way. One example is if you fill an entire SD card with images from a trip, you could lock it to prevent accidentally taking more and overriding any photos.


microSD cards: Dimensions and use cases:


0.56 x 0.43 x 0.039 inches or 15 x 11 x 1 mm


Use cases

microSD cards cover just about all other use cases. These include but are not limited to:

  • Drones
  • Smartphones
  • Go Pros, Point and Shoot cameras, and other compact cameras
  • Tablets
  • Many other mobile devices!

The locking toggle

microSD cards do not inherently have this physical feature however if they are used with an adapter, this feature can be accessed.

microSD adapter with locking toggle

Now that we know the main differnces between SD and microSD cards, it's time to delve into the markings you may see on each card and how to determine what they all mean!

This guide was first published on Sep 28, 2021. It was last updated on Mar 08, 2024.

This page (SD vs microSD) was last updated on Mar 08, 2024.

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