What is a flash memory card and what types of flash cards exist?

A memory card (also referred to as a flash card, flash memory or flash memory card) is a small portable data storage medium that is commonly used in an electronic device for storing almost all types of data: photos, videos, music, documents, games and programs. Essentially, it’s a chip (a set of electronic circuits) that allows writing and rewriting data multiple times.

Memory cards vary in shape, size, storage capacity and compatibility. They can serve as a main data storage or as a storage extension in devices like mobile phones, laptops, tablets, digital cameras, camcorders, drones, MP3 players, game consoles, printers and others.

Last update: December 30, 2021

Time to read: 7 min

What differs flash memory cards from other data storages?

Flash cards are small (most of them are not bigger than a thumbnail) and convenient to use. Unlike hard disk drives (HDDs), memory cards do not include moving parts and that’s why they are considered to be much more resistant to mechanical shocks and temperature fluctuations. Yet, they are not so resistant as USB sticks because of the lack of an outer plastic or rubber case.

In addition, a flash card can be easily removed from an electronic device. However, compared to a USB stick that is plugged directly into the PC’s USB port, a memory card generally requires a card reader to be connected to the computer. While some modern electronic devices like laptops or tablets have built-in card readers, in most cases you need an external one to get access to your memory card’s data from a PC.

And in contrast to thumb drives that are compatible with any device provided with a USB port, flash memory cards can’t be easily swapped from one gadget to another, as different devices usually require different types of cards.

What are the main types of flash cards?

In recent years, the variety of flash card types has reduced significantly due to the standardization. At the moment, the most widespread ones are SD, Memory Stick and CompactFlash. They also have some more or less popular sub-variants (for example, in case of Memory Stick, they are Memory Stick Duo, Pro Duo, Pro-HG Duo and Micro M2). And less common, but still used varieties are xD Picture Card, MultiMediaCard (MMC) and SmartMedia.

The first one in the list, SD or Secure Digital, has already become a standard for the industry. This technology is used by over 400 brands and can be found in more than 8,000 models of electronic equipment. SD flash cards come in various capacities, speed classes and formats.

The Memory Stick card format was invented by Sony and can be found in its devices released before 2010. CompactFlash has been developed specifically for digital cameras and now the cards of this type are used in high-end digital single-lens reflex cameras.

Generally, every device is compatible with some specific variety of memory card. Still, some of them may have a single universal or even several separate card slots that accept different varieties of flash cards.

What is the difference between miniSD, microSD, SDHC, SDXC and SDUC?

A wide selection of sizes, capacities and designs has made SD cards common for practically all types of gadgets from cameras to MP3 players. At present, a user can choose among:

  • miniSDs that are based on the SD technology, but are smaller in size than the regular-size SD flash cards. They are typical for portable devices like mobile phones and MP3 players and are commonly sold with a special adapter to be easily inserted in a regular SD slot;
  • microSDs (also known as T-Flash and TransFlash) that are even smaller than miniSDs and have almost replaced them in smartphones and tablets;
  • SDHC/microSDHC cards (Secure Digital High Capacity) with a file system (FAT32) different from the system of regular SD cards (FAT16) and capacities of up to 32 GB;
  • SDXC/microSDXC flash cards (Secure Digital eXtended Capacity) with up to 2 TB of capacity and exFAT file system by default;
  • SDUC/microSDXC memory cards (Secure Digital Ultra Capacity) with exFAT and a large capacity of up to 128 TB.

As for the compatibility, old SD-slots do not accept new-generation memory cards like SDHC, SDXC or SDUC. Still, the majority of SDXC cards are backward compatible with SDHC slots that, in their turn, accept SDXC cards, provided they are previously reformatted to FAT32. Nevertheless, please note that some SDXC-compatible slots are programmed to expect exFAT on cards of 32 GB and more, and may not accept SDXC cards that have been reformatted to FAT32.

SD flash cards also range in write speed classes:

  • Class 2 – from 2MB/s;
  • Class 4 – from 4MB/s;
  • Class 6 – from 6MB/s;
  • Class 10 – from 10MB/s.

And one more variant of SDs’ classification: depending on the read/write speed, new-generation cards (starting from SDHC) are divided into UHS-I (Ultra High Speed) of up to 104MB/s, UHS-II of up to 312MB/s, UHS-III of up to 624 MB/s and SD Express with a maximum of 985 MB/s.