What to Know When Choosing an SD Card?

Nowadays a lot of SD memory cards are presented on market, manufacturers have a tough competition to get the attention of the user. The models differ by format, class and due to this — by read and write speeds. But what is the real difference? This time we will talk on basic things which you might need to know while choosing an SD card.

Choosing an SD Card: What to Know?

So, you decided to purchase an SD memory card for your camera, tablet, smartphone or other device and want to know the important things to make a right choice.

Choosing an SD Card

In the below part we will take a closer look on different types of SD memory cards.

SD Card

SD (Secure Digital Memory Card) is a first secure memory card, which was designed in 2001. Over years a lot of SD modifications arrived, but right now it’s one of the most used type of memory card. SD is compatible with devices that support SD, SDHC, SDXC.

  • Maximum capacity: 4 Gb;
  • Transfer speeds: 12,5 MB/s;
  • Default file system: FAT.


SDHC (SD High Capacity) is a next generation of high capacity SD card. It’s important to mention that this type of card is not backward compatible with SD compatible devices.

  • Maximum capacity: 32 Gb;
  • Transfer speeds: 12,5 MB/s;
  • Default file system: FAT32.


SDXC (SD Extended Capacity) is another type of high capacity SD memory cards, with extended space. This type of cards has different file system and won’t work with devices which are SD compatible only. Devices manufacture under 2010 should be also compatible with this format: to make sure that your device is compatible with this format you should check if SDXC logo is present on the card’s surface. It’s important to mention that the card reader that supports SDHC and lower won’t work with SDXC memory cards (this format is incompatible with some OSs).

  • Maximum capacity: 2 TB;
  • Transfer speeds: 25 MB/s;
  • Default file system: exFAT.


SDHC I, SDXC I, SDHC II, SDXC II – memory cards with UHS (high-speed SD bus interface to enable high-speed data transfer). In order to achieve the best speed, you need to use such cards with UHS compatible devices.

UHS I defines 2 bus architecture options for up to 50MB/s (UHS-50) and 104MB/s (UHS-104). Such memory cards using the four-bit transfer mode. Usually if you have a UHS-I compatible memory card or device, you can find a mark “UHS-I” or “I” on it.

UHS II – the next generation memory cards which are also define 2 bus architecture options for up to 156 Mb/s and 312 Mb/s. UHS II memory cards using the four-bit transfer mode too. UHS II is fully compatible with UHS-I devices and backward, but you will be limited to the lower characteristics (in such case UHS-I). In case you are looking for a good way to optimize your camera’s performance – it’s recommended to purchase UHS-II memory card (like Sony Memory Card 64GB or SanDisk 64GB Extreme PRO). For pros it’s recommended to purchase a professional memory card which allows to capture high-quality images and extended lengths of stunning 1080p full-HD (like Lexar Professional 633x 128GB SDXC).

The UHS Speed Classes defined by the SD Association are UHS Speed Class 1 (U1) and UHS Speed Class 3 (U3). U1 and U3 can be applied to UHS Bus IF product family (UHS-I, UHS-II & UHS-III).

Sizes of SD Cards

Most often, the SD is used on portable devices and there are 3 different sizes. It’s important to mention that SD, SDXC and SDHC have the same form, but that doesn’t mean that these types of card will fit a regular SD slot.

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choosing sd card

Let’s take a detailed look on each of the sizes:

SD Card

Standard SD memory cards measure 32x24x2.1 mm, they weigh about 2 grams and right now are the largest one. Nowadays almost all consumer digital cameras still using standard SD memory cards (you can easily recognize them by well-known “cut corner” design).

MiniSD Cards

These miniSD memory cards are smaller than usual SD cards. miniSD weigh less than SD (about 0.8 grams) and measure 21.5x20x1.4 mm. Nowadays it’s pretty uncommon card size (it was designed to use in smartphones, but never came popular).

MicroSD Cards

microSD card has the smallest size among the SD cards. It has 15x11x1 mm and its weigh is only 0.25 grams. Commonly this type of card is used in most modern smartphones, tablets and cell phones that support SD. By using a special adapter, you can plug microSD into a standard SD memory card slot.

Tip. When choosing an SD card and its size, you must take in consideration what fits into slot of your device!

SD Card Speed Class

Now let’s take a look at what does the speed class of the memory card actually means. This one gives user information about the minimum writing speed of the memory card. The higher class SD card allows you to manipulate more amount of data, play big size audio/video files without delay and avoid other speed related issues.

Difference Between Speed Classes of SD Memory Cards

In order to make easier for users to understand how fast is the specific card while choosing an SD card, the SD Card Association implemented industry-leading memory card standards – SD Speed Classes.

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Additionally, you can check information about speed by taking look at a special description. Nowadays these speeds are growing faster, but right now you can find cards from 6x to 633x (1x = 150 Kb/s).

According to the standards of SD Card Association all memory cards have the next speed classes:

  • SD Class 2: writing speed is not less than 2 Mb/s – description 13;
  • SD Class 4: writing speed is not less than 4 Mb/s – description 26;
  • SD Class 6: writing speed is not less than 6 Mb/s – description 40;
  • SD Class 10: writing speed is not less than 10 Mb/s – description 66;
  • SD Class 16: writing speed is not less than 16 Mb/s – description 106.

Speed classes are also differ by UHS speed class (I and III) and Video Speed Class (v6, v10, v30, v60, v90).

SD class is one from the most important factors while choosing SD card, but nowadays some of us facing with cards that don’t meet the speed class that is specified.

In order to identify description of SD memory card more accurately, you can make your own test with the help of card reader and appropriate program (for example, on Windows machine try to use H2testw; on Linux use F3).

SD Speed Class is extremely important while working with HD-video, because in such case device using SD card to save data in live mode and having a high writing and reading speed becomes extremely important. That’s why we recommend you to take a look at your device’s specification and check the lowest SD Speed Class that is compatible with your device. Usually SD Speed Class is marked with “C” for common cards and with “U” for UHS standard.

choosing an sd memory card

Device’s Compatibility with SD Memory Card

SDXC memory cards are compatible only with SDXC devices, and won’t work with SD/SDHC. Meanwhile SDXC devices are compatible with SD, SDHC and SDXC memory cards.

SDHC host devices are compatible with SD and SDHC memory cards, meanwhile you can use SDHC cards with SDHC and SDXC compatible devices.

That’s all! Hope this post will be useful for you and help you choosing an SD card for your device.

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