Whether in drones, cameras or smartphones, memory cards are essential data carriers. However, the numerous formats and speed specifications can be a bit confusing. We try to shed some light on the darkness with this guide.
The most common card is the SD memory card. It is widespread and has largely supplanted earlier formats, such as the Sony memory stick. The little sister is the micro SD card. It is compatible with the SD card and can be easily used in SD slots with an adapter.
Compact Flash cards are popular in the professional photo environment. Their time is running out slowly, however, they simply do not reach the speed of an SD card. In the professional sector, CFexpress wants to become the new standard. The cards use the speed of PCIe and the NVMe protocol. This means that data rates of up to 2 GBit / s are theoretically possible. In practice, there is a lack of cameras and card readers that can keep up with this speed. The provides more details heise + article Eight memory cards in CFexpress format for professional cameras in the test.
For everyday life and the hobby, CFexpress should not play a role for a long time. We therefore limit ourselves in this article to the SD cards and the smaller micro SD cards.
In addition to the size, it is primarily the classified speed that determines the price of the card. And this is where things get complicated, as the numerous prints on the cards show. There is a speed class, a UHS speed class and a video speed class. These formats have developed over a longer period of time, and some of them can also be attributed to marketing.
First the speed class. It divides the cards into 2, 4, 6 and 10. This is the minimum speed in a worst-case test, the specification is in MByte / s (not MBit / s). The fact that the limit is 10 MB / s (or 80 MBit / s) already shows that the standard is significantly older. In fact, there is no real reason to go for a class slower than 10, especially since Class 6 cards offer a maximum of 32 GB of storage. Say: Class 10, ignore everything else.
The next class is the UHS Speed Class, which was introduced in 2009. They tie in with the first Speed Class. UHS-1 manages at least 10 MByte / s, UHS-3 is 30 MByte / s. These cards require a special UHS bus, which is now standard.
These interfaces also became too slow for 4K and 8K films, so the Video Speed Class was introduced. It’s easy to explain: It is made up of a V followed by a number. The number indicates the minimum sequential write speed. V10 creates 10 Mbytes / s accordingly and is on the same level as Class 10 and UHS-I.
|2 MByte/s||Class 2||❌||❌||SD recordings|
|4 MByte/s||Class 4||❌||❌||HD-Ready / Full-HD|
|6 MByte/s||Class 6||❌||V6||HD-Ready / Full-HD|
|10 MByte/s||Class 10||U-1, UHS-I||V10||Full HD, higher frame rates with 60 and more fps|
|30 MByte/s||❌||U-3, UHS-III||V30||4K recordings, 60 or 120 fps|
|60 MByte/s||❌||❌||V60||8K recordings|
|90 MByte/s||❌||❌||V90||8K recordings|
In addition to the notation SD and Micro-SD, the abbreviations SDHC and SDXC are often used. These are primarily techniques with which a higher capacity for SD cards is written. SDHC allows up to 32 GB of space, with SDXC even up to 2 TB of memory is possible on the card. However, these cards must be supported by all devices in the chain (i.e. cell phones, cameras and readers).
Does something speak against Micro-SD in the SD adapter?
Is there a reason why you shouldn’t use a Micro-SD permanently in an adapter? In fact, we found a minimal loss of speed in our own benchmarks. However, it was so low that it is within the normal measurement tolerance. Further research in relevant photo forums and sites did not provide any information either. Micro-SD to SD adapters are purely passive, there are actually no components that can break. Most forums do not recommend this, but for no specific reason. Some believe that if the cards are used for a long time (i.e. 4K / 8K video recordings) they could become warmer and therefore slower and more error-prone, there is no concrete evidence of this.
In our experience, nothing speaks against using a micro SD card in a single lens reflex camera for normal recordings. For long series recordings or UHD videos, you should do a test beforehand and then decide for yourself.
Recognize fake size information
Again and again, stories about memory cards with falsified sizes make the rounds. One should be suspicious of particularly cheap, large cards. But it doesn’t hurt to briefly check every new purchase before using it productively. Because the forgeries pretend that they just keep writing data, but in truth the content is lost. in the heise article Counterfeit USB sticks and SD cards: What to watch out for colleagues explain how to identify incorrect memory and use the tool H2Testw can query the capacity. If you buy the sticks from an EU dealer, you can return them within 14 days.
Which memory card should I buy?
To make it simple: If you are primarily looking for data storage for your mobile phone or individual photos, you can use a Class 10, UHS-1 (U1), V10 memory card. These are the cheapest memory cards, but you can work solidly with them.
The term becomes relevant when you want to record longer videos with a 4K resolution or high frame rates. A UHS-3 (U3), V30 card should be used for 4K 60/120 fps. A minimum speed of 30 Mbytes / s leaves enough buffer to capture all recordings on the card.
If you record in 8K (or want to be on the safe side with 4K), you should pay attention to the video speed class and choose a card with V60t or V90. As long as you have a reasonably up-to-date device, faster cards shouldn’t be a problem. They are backwards compatible, but you should pay attention to the file size. If you format your card with FAT32, you can record a maximum of 4 GByte. Many devices circumvent this limitation by taking a short break every few GB, but then you can lose content. Formatting is better than exFAT, but then you should save the data quickly, the format is considered prone to errors. More about this in heise tips + tricks article exFAT vs. NTFS – these are the differences.
Memory cards are flooding the market. The good news is that even the cheapest models are sufficient for normal use in cameras or smartphones. Only when you record in 4K or 8K do you really have to pay attention to the speed.
It is also good practice to send a new memory card through a test first. This finds fakes and can also point out defective sectors. This is especially important in cameras, after all, photos or videos can only rarely be restored.