How to correctly select a micro SD card? Differences between SDHC and SDXC

Source:   Editor: Jacquelyn Update Time :2019-03-13

Today, smartphones and tablets are demanding more and more storage space. Even mobile phones with capacity of 32 GB above still don’t satisfy their requirements. However, for most users, not too many applications and games installed, but too many personal data or multimedia content stored, including photos, music, movies or other documents, causes 64 GB storage space be full.

Therefore, when storage space is insufficient or nearly exhausted, most people choose to insert micro SD card to expand additional storage space among various ways. After all, this is one of the simplest ways.

Of course, not all smartphones and tablets support micro SD cards, such as iPhone and iPad. However, many Android devices on the market support micro SD card extensions, even the declining Windows plus Phone and BlackBerry phones.

It's easy to know whether a computer supports a micro SD card or not. Look at the introduction of official website or the complete specification of mobile phone. However, today many mobile phones that support the expansion of micro SD cards do not necessarily provide a separate micro SD card slot. Generally, nowadays many of them put micro SD and SIM card together.

Simply put, the location of micro SD card is also provided separately on the slot of nanoSIM card.

However, it’s a problem for a large number of mobile phones novice how to choose a suitable micro SD card? At present, there are many kinds of micro SD cards on the market. Different prices, capacities, types and brands vary. How to choose the right equipment or meet personal needs? Here's a brief talk (experienced friends can ignore the following).

Differences between SDHC and SDXC

SDHC is short for Secure Digital High Capacity, while SDXC is Secure Digital Extended Capacity.

Specific definitions are not explained much here. The only real difference between the two is the range of data that can be stored. The storage capacity of SDHC type micro SK card ranges from the smallest 2GB to the highest 32GB, while that of SDXC type micro SD card ranges from 32GB to 2TB. The largest micro SD card we have seen so far is 512GB.

Speed levels between Class and UHS

SD Card Association has two terms to define the speed level of micro SD cards, where class refers to "speed level". Each level mark refers to the minimum transmission speed of this card. For example, Class 4 represents 4MB/s, Class 6 represents 6MB/s, and so on.

UHS means "Ultra + High + Speed" and "UHS speed level" differentiates micro SD cards with lowest writing speed. For example, UHS-I 1 has the lowest writing speed of 10MB/s, while UHS-I 3 has the lowest writing speed of 30MB/s.

The following is the minimum writing speed for different speed levels of micro SD card:

It is important to note that actual speed of most micro SD cards is necessarily much faster than the lowest speed labeled. For example, Class 10 micro SD cards can provide 95 MB/s, while UHS cards can reach at 312 MB/s.

There is no corresponding relationship between Class and UHS. However, in terms of speed, Class 2, Class 4 and Class 6 are just general speed levels. Class 2 is suitable for low-resolution video, while Class 4 and Class6 are suitable for HD or 1080p full-HD video. Class 10 is faster than the front three, and is suitable for 1080p full-HD video recording or continuous HD static pictures.

As for UHS, UHS-I 1 can only satisfy 1080p full-HD recording or continuous high-definition static picture shooting, and only UHS-I 3 can meet the demand of 4K+2K resolution video recording.

Application performance class

At the end of last year, SD Card Association also introduced a new standard called “App Performance Class”, which aims to highlight the use scenarios of micro SD cards for mobile devices such as smartphones or tablets, and ensure that applications can run with the best performance and meet the technical market demand. Therefore, such micro SDs can not only store pictures, videos, music, files and other information, but also run and store applications.

App Performance Class1 short for A1 is the most basic class. Micro SD cards marked with A1 must meet or exceed the following performance under specific conditions:

- Input and Output Operation Per Second (IOPS) is 1500 times. 

- Writing operation per second is 500 times.

- Stable continuous reading speed is 10 MB per second.

Micro SD cards marked with A2 must meet or exceed the following performance under specific conditions:

- Input and Output Operation Per Second (IOPS) is 4000 times.

- Writing operation per second is 2000 times.

- Stable continuous reading speed is 10 MB per second.

A1 or A2 is basically enough to meet the ideal speed of opening applications and processing tasks. Android 6.0 Marshmallow has begun to supported to use micro SD cards as "Adoptable Storage", that is built-in storage, and at that time, A1 and A2 have done requirement testing for minimum execution time.

How to choose micro SD card

Obviously, everyone wants micro SD card with fastest speed, highest capacity and lowest price. There are many brands on the market such as Samsung, SanDisk, Toshiba, Kingston and Lexar. In fact, after understanding the basic knowledge of above micro SD card, I believe that self-selection is no longer a problem.

For example, it’s not a problem for a micro SD card labeled with Class10 or UHS-1 with a maximum speed of 80 MB/s for basic 1080p video recording. The storage card marked with SDXC, UHS-II or 100MB/s is suitable for 4K video recording. In fact, there are already many micro SD cards with A1 symbols on the market, but they are relatively expensive, because 32GB costs about $1.2 and 128GBGB is about $44.8 at least. But if having a need for application performance, you should give priority to such micro SD cards, which can ensure that mobile experience is not hampered by SD cards.

In addition, purchasing micro SD card still needs to consider brand reputation and user testing. The key is that the warranty terms must be good, in case something goes wrong.

Of course, you should be careful where you buy it. Some people want to choose the cheapest one in Taobao. After checking the reviews and find that it is a bad or false micro SD card, you will regret.

Before buying a micro SD card, you must check the official complete specifications or read the instructions for using mobile phones to ensure that micro SD card is compatible with your own devices. Even without these conditions, you should also ask the official customer service. Finally, Lexar's micro SD card must be abandoned because this brand has terminated its retail business and is about to go bankrupt.

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