Sd Memory Card Symbols and Acronyms: Understanding Them to Buy Well


Guide updated on 19/06/2019 with the addition of the future SDUC format and the Express Bus –Like many areas of consumer electronics and IT, products are all marked with acronyms, symbols and logos which, although they all have a meaning, are cruelly lacking in transparency. They are, however, of crucial importance in choosing the product that suits you best. This is the case, for example, with SD cards (acronym for Secure Digital), which are full of information, often redundant.

The memory card is an important element. Not only does it store your content, but it backs it up in often extreme conditions. So how can you choose one card over another if you can’t tell them apart by looking at packaging ? Here are all the keys to understanding. Acronyms and symbols on an SD and micro SD memory card fall into two categories. Those related to capacity and those related to flow.

But first, a little clarification: the difference between SD and micro SD cards lies in their size, as micro SD cards are logically smaller. There were also mini SD cards but these have disappeared. Today, SD cards are primarily intended for use in cameras or computers, while micro SDs are mostly found in smartphones or connected objects. They are also found in some small format cameras such as the GoPro.

acronyms-symbols-memory card-sd-micro-sd

A History of Capacity

SD:The SD format is the most classic. It is also called SDSC, SC stands for“standard capacity”. The file system here is FAT16. It is compatible with all SD players. The maximum capacity is 2 GB.

SDHC:The SDHC format, for High Capacity, is the first evolution of the SD format. The file system here is FAT32. Its capacity is 2 GB minimum and 32 GB maximum. Recent players are all compatible with this format.

SDXC:The SDXC format, for Extended Capacity, is the second and latest development to date. Its capacity varies from 32GB to 2TB, but there is not (yet) any card with a capacity greater than 1TB. The file system here is the exFAT which offers excellent performance. There are now many compatible products. 

SDUC: The SD Association announced in 2018 a new specification to succeed the SDXC, the SDUC for“ultra capacity”. These cards will have up to 128TB of storage depending on the features validated by the association in charge of the standard, but don’t expect such capacities for years to come. Moreover, no SDUC card is available for sale at the moment.

A History of Speed

There are several types of class abbreviations. It is either an even number surrounded by a C (the class), or an odd number in a U, or a two-digit number with a V, or a number with an x. In the latter case, the x replaces an equivalent unit of 150 Kbps. For example, a rate of 13x corresponds to 13 times 150 Kbps, or 2 Mbps. All these abbreviations indicate the same information: the guaranteed Minimum write throughput. Here’s what they mean: 

Class 2:This is the minimum class of an SD card. It guarantees a throughput of 2 MB/s. This corresponds to a 13x rate. These cards are only useful for recording 480p videos.

Class 4:The second class of SD card guarantees a writing speed of 4 MB/s. The rate equivalence is 26x. These cards are useful for 720p recording.

Class 6:The third class of SD card offers a write speed of at least 6 MB/sec. The rate equivalence is 40x. These cards are used to record 1080p video but are still capable of recording in 4K, although they are not the most suitable for this purpose.

Class 10 / U1:The fourth class of SD card guarantees a write rate of 10 MB/s, i.e. a transfer rate of 66x. Note that Class 10, SD and SDHC formats, and Class U1 (or UHS 1), SDXC format, offer the same warranty. They are used for recording in RAW, AVCHD, with a resolution of up to 4K.

Class U3:The fifth class, of UHS type, concerns the SDXC format. It offers a minimum throughput of 30 MB/s. It is perfect for handling the data flow imposed by a 4K recording.

Class V6: The V classes, called video speed classes, are the most recent. A V6 card offers a minimum writing speed of 6 MB/s, just like C6 cards, they can record in 4K even if a higher speed is recommended for this purpose. 

Class V10:Once again, Class V10 cards are equivalent to C10 or U1 cards, so they offer a throughput of 10MB/s and can record videos with up to 4K image resolution. 

Class V30:Equivalent to class U3, the V30 cards offer a minimum write rate of 30 MB/s, a comfortable speed for 4K.

V60 Class:With V60 cards, sold at fairly high prices, a Minimum write speed of 60 MB/s is achieved, enough to allow 8K video recording. 

Class V90:  These are the most high-end SD cards available today. Very expensive, their minimum bit rate is 90 MB/s, allowing 8K video recording and high frame rates. 

Which bus do we take?

Acronyms I and II:  These Roman numerals are sometimes found on some SD cards. They indicate the interface version of the card. The I corresponds to the UHS-I bus which goes up to 50 MB/s for writing and 104 MB/s for reading. The number II corresponds to the UHS-II bus, which is three times faster. If these symbols are not written on your SD card, then the bus is older and less efficient.

EX (Express):This is the bus of the future, announced at the same time as the SDUC format. It is not yet available for sale but promises much higher performance than UHS-II cards. EXs are based on the PCI Express interface and NVMe protocol used for computer SSDs. This should enable them to achieve a maximum data transfer rate of 985 MB/s. Bonus: this bus will not be reserved for SDUC cards but will also arrive on lower formats. 

A History of Prices

The price of a memory card varies from a few euros to more than a hundred euros. The price increases not only according to the capacity, but also according to the class and the throughputs supported. We have selected a few SD cards of different classes and offering good to excellent read and write speeds on three storage capacities, 32, 64 and 128 GB.

In our selection, the SanDisk Ultra SDHC (32GB, 30MB/s) is the price/performance choice, while the Lexar Professional (32GB, 300MB/s and 128GB, 95MB/s) and Transcend Ultimate (64GB, 90MB/s) SDXCs will speak to the discerning user.

For smartphones and/or action cams, a microSD format card is required. Note that these cards come with an SD card adapter, making them more flexible and versatile. Versatility and compactness at a price, these microSDs are more expensive than SD cards.

We have selected the best on the market, always in 32, 64 and 128 GB. The 200GB and 256GB microSD cards are designed for the very large content consumers, or those who want to capture long video sequences in UHD / 4K. There are also bigger capacities but here you really have to break your piggy bank.

Delkin microSDXC 64 GB (V60 – UHS-II)

Remember that all these cards are based on Flash memory technology. While this format is less sensitive to shocks than a conventional mechanical Hard Disk Drive it remains sensitive to temperature, humidity and magnetic fields.

The number of write and erase cycles is limited and some cards do not handle wear well. This exposes your content to the risk of deletion, which is why you should buy a reliable card from the start.

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