A Guide to SD Card Types

These days, there are almost limitless options out there when it comes to local data storage. SD cards and Micro SD cards have become standard in all kinds of portable devices due to their affordability and practicality. Some high-end SD cards can even hold capacities and transfer data at speeds rivaling internal hard drives. Devices like phones and cameras can double or sometimes even triple their storage capacity through the addition of an SD card.

Choosing the right SD card for you, however, can get confusing because of the high number of options and form factors available. Learning the differences between each and what devices they are compatible with will help you make the best decision possible when purchasing your next SD card. Here is a comprehensive guide to the various types of SD cards available on the market today.

SD Cards are composed of flash memory. There are two types of flash memory: NOR, which is physically larger, and NAND, which is smaller and has faster read/write speeds. NAND is the perfect medium for SD cards because NAND memory can retain data even when the power is off. NAND is a non-volatile, persistent data storage system on solid-state. It has no moving parts and is less prone to breaking.

There are multiple types of SD cards to choose from. The best place to start when shopping is with the form factor. Specific devices such as cameras or smartphones will only support a particular form factor. Ensuring you know which SD card your intended device supports is crucial to compatibility. You should always check compatibility with the exact device you are buying an SD card for. Read below for a list of the form factors and devices commonly supported by each:

Also referred to as full size, standard SD cards have dimensions of 32mm x 24mm. They are used in high-end recording devices such as DSLR cameras or professional-grade video cameras. Many computers and laptops have SD card readers that fit a full-sized card or Micro or Mini SD card using an adapter.

By far, the most common SD card form factor is Micro SD. These devices are in almost every cell phone in the world and allow for the easy transfer of user data between phones, computers, and many other devices. As the name implies, Micro SD cards are incredibly small. The dimensions of a Micro SD card are 15mm x 11mm. Most Micro SD cards will come with a standard-sized adapter so they can connect to computers and other devices more easily.

While not very common by today's standards, it is still important to learn about Mini SD cards. Released in 2003, the Mini SD saw use in many portable devices such as cameras and early smartphones. With a 21.5 mm x 20mm size, Mini SD is smaller than standard cards but still significantly larger than Micro SD. The smaller size made Mini SD a popular choice for much of the early 2000s, but after the release of Micro SD cards in 2005, Mini SD cards saw a rapid decline in use. Today it is rare to find a device that still supports Mini SD cards without an adapter. 

Exclusive to high-end cameras or very specific devices, compact flash memory is larger in physical size than any SD card but offers other benefits to users. In the past, compact flash memory was the only way to get large amounts of fast digital storage on a camera. Although in recent years, SD cards have rivaled compact flash memory in terms of max storage size and read or write speeds.

Once you know the form factor of the SD card you need, you can focus on other specifications to find the best option for you. SD cards of any shape and size will operate in the same way, so there are some key terms and features to be aware of when shopping. Here’s what you need to know about SD card specifications:

Often referred to as the size of the SD card, the capacity actually has nothing to do with the physical form factor. Capacity when discussing SD cards refers to the maximum storage size of an individual card. For example, multiple Micro, Standard, or Mini SD cards could all have the same capacity of 1GB. A great way to determine what size SD card you need is by analyzing the type and amount of data you need to store. Videos require much more space than photos on SD cards, and both mediums quickly grow in file size with higher resolutions. 

How fast an SD card can read and write data is referred to as the device's speed. Specific tasks such as HD or 4K video recording may require higher read or write speeds. The speed of an SD card is measured using a class system denoted on the card by a number within a small circle. These distinctions can get quite complex and are ever-changing. For most users, knowing the cut-off speeds for HD and 4k video recording is more than enough information to find the proper card. An SD card needs a write speed of 4MB/s or higher, also known as Class 4 or higher, to record HD video. The recording of 4K video requires 30MB/s or higher write speeds, or what is called a UHS Class 3/III rating. 

Arguably as important as the other specifications, compatibility tells you far more than just if the SD card will work with your device.  Older devices may support newer SD cards but require limitations to do so. For example, a lightning-fast new SD card may work in an old digital camera. However, the inherent design of the old device will only allow the card to function at reduced speeds. Older cameras may also have hard limits on the max storage size supported by the device, thus limiting the functionality of larger cards. Learning more about the compatibility of the device you intend to use with an SD card will ensure that you make the most affordable and efficient choice possible.

Unfortunately, purchasing an SD card is not as simple as looking for a labeled size and speed. There are many types of cards out there, and minor distinctions between each. Please read below for a list of the most common types of SD cards, their naming conventions, and what they mean.

These days, the original chunky and severely limited standard SD card is uncommon but still supported by some devices. Labeled simply as SD, these cards have a maximum capacity of 4GB and a top speed of 10MB/s. The one benefit of these cards today is that if a device does support using them, standard SD cards are now tremendously affordable.

While SDHC cards have faster read and write speeds than standard SD cards, that is not their most desirable feature. Secure Digital High Capacity or SDHC cards' primary focus is on storing larger amounts of data. These cards are pretty common today, and anything with over 4GB of storage can be considered an SDHC memory card. The maximum amount of storage available on an SDHC device is 32GB.

Starting at 64GB and going all the way up to 2TB (2000GB), Secure Digital eXtended Capacity or SDXC cards are some of the highest-quality storage options on the market today. Perfect for recording high-resolution video or storing large amounts of photos, these cards are tremendously popular within many professional industries. The maximum transfer speed of 90 MB/s also makes SDXC cards necessary for anyone working with 4K media. 

SD Ultra Capacity Function was developed to handle storage requirements of 3G, 4G and 5G mobile phones, along with other consumer and industrial uses (like the Internet of Things, dashcam recordings, or virtual reality and augmented reality) which requires large-volume storage. SDUC can store between 2TB and 128TB. The increased capacity is a result of advances in NAND technology, which enabled layer-stack-mounting that allows small memory cards to store multiple terabytes of data.

The increased demand for video streaming contributed considerably to the origination of the SDUC option. Currently, 4K video is the standard for streaming video services, but 8K video will become more readily available once Internet Service Providers and mobile carriers are able to improve internet capabilities to support streaming data without compressing it.

Functioning almost identical to a standard SD card, the only significant difference of a Micro SD card is its size. Although the reduced size of Micro SD cards has helped them stay relevant and see use in a wide range of devices to this day. Micro SD cards also have a slightly higher maximum capacity of 16GBs. Almost every smartphone has or supports the use of a Micro SD card. 

Introduced in 2007, Micro SDHC is simply a newer and slightly improved version of Micro SD cards. These cards can store up to 32GB of data and have a top transfer speed of 10MB/s. Like SDHC and SD in standard cards, SDHC Micro has become common and replaced traditional Micro SD cards in many situations. It is important to note that older Micro SD devices often do not support the use of Micro SDHC cards.

Just like with full-size cards, the highest quality Micro SD cards are also called SDXC. Storage capacity on these cards ranges from 32 GB to 2 TB, and they have the same 90MB/s transfer speeds as their full-sized counterparts. The storage sizes made possible by Micro SDXC cards make them ideal for gamers and other users needing to store massive amounts of data. The one drawback is that devices require specific Micro SDXC slots to utilize these powerful memory cards.

Like SD Ultra Capacity Function cards microSDUC supports between 2TB and 128TB of memory. Although all microSD cards will physically fit into all microSD card slots, not all microSD cards are compatible with every slotted device. MicroSDUC cards will only work in microSDUC-compatible devices. 

Compact Flash is a flash memory card format often used in DSLR cameras. It is larger in physical size, capacity, read speeds and write speeds compared to other SD cards. It is also less prone to damage due to its construction. However, it is also more expensive than your typical SD Card. Since it is one of the older SD Card form factors, Compact Flash's predecessor, CFast, was developed to achieve even faster speeds due to its Serial ATA (SATA) interface. Compact Flash and CFast are used in older, high-end cameras to shoot hi-res images and video, but aren't as mainstream as SD cards. 

SD cards come in a variety of shapes and sizes. Beyond compatibility, the many names and specifications of SD cards can also tell you what tasks an individual memory card may excel in. Depending on what you intend to use an SD card for, there will most likely be an optimal choice for you. Learning the differences between each type of SD card and how they are most commonly used will give you the best idea of what kind of card you need. Remember, there is more to SD cards than just the storage size, and multiple cards may be sufficient for a single device. Adapters can also help you to transfer data or use SD cards in a broader range of devices.