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Ultimate guide: how to choose SD memory cards, micro SD cards and more

Choose memory cards for a camera, camcorder or other device not as simple as it used to be.

There are various types of cards, with different speeds, capacities and characteristics, apparently similar to each other but very different when examining parameters such as read / write speed, resistance, quality and operating conditions. Many abbreviations appear on the packaging or on the cards of the various manufacturers and with this article we will try to clarify illustrating their meaning.

The capacityDevice manufacturers use compression codecs (e.g. MPEG-4, H.264, etc.) and different bit-rates, which lead to variable file sizes and it is not easy to indicate exactly how many hours of movies or how many photos can be stored. on a memory. Obviously the larger the storage capacity, the greater the number of photos / movies that can be stored.

always good to check the manual of your device: some old products may not be able to recognize large "cuts" of memory.

Secure Digital cards (SD, SDHC, SDXC, microSD, microSDHC, microSDXC)

Secure Digital technology, introduced way back in 2001, derives from the MMC MultiMediaCard standard. SD cards are slightly thicker than original MMC cards. This means that devices designed to support SD cards are able to accept MMC cards as well unless the host device is strictly limited to SD cards.

In addition to the standard SD cards, the various manufacturers have long offered high-performance SD cards, ideal for capturing high-resolution videos. SDHC (Secure Digital High Capacity) cards start at 4GB, while SDXC (Secure Digital Extended Capacity) cards start at 64GB: both solutions offer greater data storage volume and optimized recording performance.

The speed classesThe SD Association defines speeds using two terms: Speed ??class and UHS speed class. The speed class represents the parameter originally used, with a following number that expresses the speed of the card: 4 for 4MB / s, 6 for 6MB / s, etc.

With the term UHS (Ultra High Speed) reference is made to the minimum writing speeds to differentiate the cards from each other. For example, the UHS-I 1 speed class has a minimum write speed of 10MB / s, while the UHS-I speed class 3 has a minimum write speed of 30MB / s.

Higher-class memory cards support high video bit rates and higher quality video recording. Class 4 memory cards are ideal for capturing HD video while Class 10, Class 1 UHS and Class 3 UHS speed memory cards support Full HD and Ultra HD 4K video capture.

The SDHC and SDXC cards indicate speed classes, called Class 4 and 10, as well as UHS class 1 and 3 speeds, which allow to obtain a minimum data transfer speed, able to guarantee optimal performance with SDHC and SDXC devices.

Although they are identical in size to common SD cards, they are designed differently and are therefore recognized only by SDHC and SDXC host devices. To check the compatibility of the card, make sure that the SDHC and SDXC logo is printed on the cards and host devices (such as cameras, video cameras, etc.).

memory cards Symbols on SD cards

The microSD cards (SDC)

MicroSD cards (SDC) represent the compact form factor of SD cards and are often those used in smartphones, tablets and other mobile devices. MicroSD cards are about the size of a fraction of common SD cards, but if inserted inside an adapter, they can also be used in standard SD device slots (for example, in Flash media readers). MicroSDHC cards offer more storage, allowing you to store more videos, images, games and any other digital content used in modern digital mobile technology.


UHS stands for Ultra High Speed. The UHS-I enabled SDHC and SDXC products are capable of supporting theoretical data transfer rates of up to 104 MB / s, four times faster than the previous possible transfer rate of 25 MB / s.

A UHS-enabled host device is required to achieve superior performance in any way. Cards that support UHS-I are compatible with previous non-UHS hosts, although performance on non-UHS hosts will be limited by the host's bus interface capability.


UHS-ll the fastest SD card interface available for communicating with camera / camcorder hosts and with computers with maximum bus interface speeds of up to 312 MB / s. Cards that support UHS-ll are compatible with previous UHS-l hosts, although performance in UHS-l hosts will be limited by the host's bus interface capability.

Normal and high-speed cards can also be used with UHS-I host devices. Higher performance enabled by a UHS-II host device can only be achieved with a UHS-II memory card.

When to choose faster cards

If you only need space and just take a few photos and shoot short videos, it is of little importance to choose very fast memory cards. Otherwise it is generally preferable to use faster cards. These allow you to minimize the waiting for reading / writing, avoid problems of file corruption as well as allowing you to shoot quickly in sequence.

Video files captured by the camcorder may be corrupt when the card write speed is not adequate; the quality of the video is automatically reduced by some devices in order to adapt to the speed of the card.

For example, a Full HD video (1080p) may be transformed into a video with a far lower resolution. In the event that the writing speed of the camera is greater than that of the Flash card, the camera pauses and the movie is stopped unexpectedly once the speed limit of the card is reached.

The problem does not only concern video cameras but also cameras. Many of these are equipped with a function that allows you to acquire a continuous sequence of images with a single press of the shutter button; in this way it is possible to photograph events or subjects that move very quickly – such as children or our four-legged friends.

If the card's writing speed is too low, you cannot use this function. Thanks to the extreme resistance and high speed of the new generation memory, it is possible to take advantage of the continuous shooting performance, greater workflow efficiency and better use of advanced functions, such as shots of more frames per second and shots continue in burst mode.

Tabs table 2


For CompactFlash cards, the important parameter to look for is "VPG" (Video Performance Guarantee). VPG-20 highlights that the Video Performance Guarantee card is enabled and allows you to record videos with a minimum write speed of 20 MB / s. VPG-65 the reference of the Video Performance Guarantee which highlights the possibility of recording videos with a minimum sustained writing speed of 65 MB / s (guarantees continuous recording of 4K and Full HD videos). In any case, performance depends on the host device.

CompactFlash table

Other parameters

Some memory cards differ from others in their ability to operate at extreme temperatures (between -25C and 85C, so that they can record videos in high definition or take photos in any climatic condition) for use in industrial environments.

Some cards have also been tested according to rigorous procedures against stress, shock and vibration or are equipped with an RTV silicone cover for added protection. The warranty varies from manufacturer to manufacturer; some even offer a limited lifetime warranty.

The brands

The best known brands for memory cards are definitely SanDisk which offers all the tags, formats and speeds for both Video-Photo and for Mobile Phones and Embedded systems, Lexar, more specialized in the photo-video field and Kingston which has a rather varied offer. Prices are very variable and it is not uncommon to find offers over 40% of the list price. For this reason, we encourage you to consult our recommendations on Hardware Offers or special discounts before purchasing.