What do symbols on micro SD cards mean?

Micro SD cards are tiny storage devices that are commonly used in smartphones, tablets, drones, dash cams, and other electronic devices. On the front and back of micro SD cards, you’ll often see a series of cryptic symbols and numbers that indicate key information about the card’s capabilities and specifications. In this comprehensive guide, we’ll decode the meaning behind some of the most common micro SD card symbols and markings.

Capacity

One of the most important specs for any memory card is its storage capacity – how much data it can hold. Micro SD cards are available in capacities ranging from 4GB up to 1TB and beyond. The specific capacity of a micro SD card is typically printed on the front, with common options including:

  • 4GB
  • 8GB
  • 16GB
  • 32GB
  • 64GB
  • 128GB
  • 256GB
  • 512GB
  • 1TB

Higher capacity cards can store more photos, videos, apps, and other files. But they are more expensive than lower capacity options. When shopping for a micro SD card, choose one that matches or exceeds the storage needs for your intended device and usage.

Speed Class Ratings

Another crucial specification for micro SD cards is their speed class rating, which indicates the minimum guaranteed speeds at which the card can read and write data. Faster speed classes allow you to snap photos, shoot videos, transfer files, load apps, and more quickly. Micro SD cards have the following types of speed ratings:

Speed Class

The standard Speed Class rating consists of a number enclosed in a C, like C2, C4, C6, etc. The number describes the minimum write speed in megabytes per second (MB/s). So a C4 card has a minimum write speed of 4 MB/s, while a C10 card can write at a minimum of 10 MB/s.

UHS Speed Class

UHS, or Ultra High Speed, is a separate speed rating for SD cards designed for intensive applications like burst mode photography and 4K video capture. UHS speed classes, designated as U1 and U3, indicate minimum performance capabilities. A U1 card should have read/write speeds of at least 10 MB/s, while a U3 card will have minimum speeds of 30 MB/s.

Video Speed Class

The Video Speed Class, shown as V6, V10, V30, V60, or V90, describes the minimum write speed when recording video. A V6 card can sustain at least 6 MB/s, while a V90 card can handle a minimum continuous write speed of 90 MB/s.

When looking at micro SD cards, choose one with a speed class rating that matches the capabilities of your device. Higher speed ratings allow you to utilize your device’s advanced features.

UHS Speed Grade

Micro SD cards that carry a UHS speed class rating may have an additional UHS speed grade designation like U1 or U3. This indicates how quickly the card can read data from its memory in order to load apps or refresh image previews.

  • U1: Sustained read speed of at least 10 MB/s
  • U3: Sustained read speed of at least 30 MB/s

A higher UHS speed grade equates to better real-world performance, so U3 is preferable over U1 if your device supports it.

Durability Ratings

Some micro SD cards also carry ratings that describe their durability and resilience to extreme conditions:

Temperature Proof

Cards with this marking are able to withstand exposure to extreme temperatures ranging from -25°C to 85°C.

Waterproof

Waterproof cards can resist damage when submerged in water.

Shockproof

Shockproof or impact-resistant cards can withstand vibrations, shocks, and drops.

X-ray Proof

X-ray proof cards are resistant to damage from X-ray machines like the ones used for airport security screening.

Durability ratings aren’t essential, but can provide peace of mind when using micro SD cards in harsh environments.

Card Format

Micro SD cards are available in three different formats:

  • SDHC – SD High Capacity cards offer capacities up to 32GB.
  • SDXC – SD Extended Capacity cards range from 64GB to 2TB.
  • SDIO – An SD Input/Output card that combines storage with input/output functions.

Most consumer devices can use SDHC and SDXC cards. But confirm compatibility before purchasing a micro SD card in one of these formats.

Manufacturer Code

Each micro SD card will be labeled with a manufacturer code printed on the front, which identifies who made the card. Here are some common manufacturer codes you may see:

  • SanDisk: SDC
  • Samsung: SDH
  • Lexar: LSD
  • PNY: PNY
  • Transcend: TSD
  • Sony: MS

While less crucial than performance specs, manufacturer codes allow you to see who produced a particular micro SD card. Leading brands like SanDisk, Samsung, and Lexar are generally well-regarded in terms of quality and reliability.

Model Number

Along with the manufacturer code, micro SD cards have a model number printed on the front that identifies the specific card version. Model numbers aren’t overly helpful in determining a card’s capabilities, but can assist with identifying counterfeit cards or verifying compatibility for a device.

Serial Number

Each micro SD card contains a unique serial number, typically printed on the back. This allows manufacturers and vendors to identify a specific physical card. The serial number is mainly useful for tracking cards in commercial or industrial environments where many identical cards are used.

Size Adaptor Code

While called micro SD cards, these devices aren’t always micro-sized. They often come with a plastic adaptor so they can be used in full-size SD slots. A size adaptor code will indicate what size adaptor, if any, comes with the card. Common adaptor codes include:

  • M3 – No adaptor included, micro size only
  • M2 – Full-size adaptor included
  • M1 – Mini-size adaptor included

Having the right size adaptor allows you to use micro SD cards in a variety of devices. But the adaptor can be removed to use the card directly in a micro-sized slot.

Fake Card Identification Code

Due to their small size and universal use, micro SD cards are unfortunately prone to counterfeiting. Some fake cards skimp on storage capacity and performance. To help identify legitimate cards, manufacturers may print a fake card identification code on the front, like:

  • h2testw
  • FAKE

These codes indicate that software like h2testw can be used to validate the actual capacity of the card and expose counterfeits.

Write Protection Switch

Many micro SD cards have a small physical switch on the side that toggles write protection on and off. When switched on, the card becomes read-only and can’t be written to or erased. This helps prevent accidental deletion of photos, videos, and other important data.

The position of the write protection switch is typically indicated by a locked or unlocked padlock icon. The locked position enables write protection, while the unlocked position allows normal read/write functionality.

Markings for Microcontrollers

Certain micro SD cards are designed to work with microcontroller devices like the Arduino. These may carry markings like:

  • Arduino
  • Raspberry Pi

These help identify cards that are optimized to work with hobbyist microcomputers and development boards.

Card Components

In addition to printed markings, there are a few physical components on micro SD cards that are good to know:

Gold Contacts

The gold strips on the bottom of the card are electrical contacts. They connect the card to the device’s SD card slot to transfer data.

Write Protect Switch

As discussed earlier, this small sliding switch enables and disables write protection on the card.

Notch

The plastic notch on the back or side ensures the card is oriented correctly when inserted in a slot. The contacts face down and the notch lines up with a ridge in the slot.

Installing in a Device

When installing a micro SD card in a device like a smartphone, camera, or dash cam, be sure to follow any safety precautions described in the product manual:

  • Power off the device before inserting the card
  • Insert gently with contacts facing down
  • Align the card notch correctly in the slot
  • Push in until a click indicates it’s locked in place
  • Avoid touching the gold contacts

Eject and remove the card before powering off the device. This avoids any chance of data corruption. Also be sure your device supports the capacity of your micro SD card before use.

Conclusion

While tiny, micro SD cards are packed with crucial specifications, ratings, and codes. Understanding the key information printed on these cards allows you to choose compatible models with sufficient speeds and capacities to match your usage needs. With this guide, you can decode those cryptic micro SD card symbols and markings to select the ideal card for your smartphone, drone, dash cam, or other device.