Selecting the right SD card helps to save cost and improve your devices’ performance. Especially when using a camera or camcorder to take videos or continuous shooting, a good SD card really matters. As SD card has been an essential storage for your digital devices by storing data, it is a necessary to know the standard of SD card classes.

How is the type of SD card classes?

Class is a guidance of speed for memory cards launched by SD Association. To distinguish SD cards among different writing or reading speed, there are various types linking to the speed ratings.

Speed Class	UHS Speed Class	Video Speed Class
“Speed Class“ Mark C10	“UHS Speed Class” Mark u3	“Video Speed Class” Mark v90

1. Speed Class – this is an older generation of speed family, the market used it in last decades. Normally number with a circular “C” symbol is telling minimum write speed.
   • Class 2 (C2): The minimum write speed is 2MB/s. This is the slowest version for this type, most SD cards in low capacity offers this speed.
   • Class 4 (C4): 4MB/s by write
   • Class 6 (C6): minimum write speed of 6MB/S
   • Class 10 (C10): minimum write speed of 10MB/S. C10 is the main demands for present devices, users prefer fast reaction.
2. UHS Speed class – It is an updated version of speed; the full name is Ultra-high speed. There is “U” symbol together with number to tell different types. Two main ratings within the UHS speed class are as follows.
   • UHS-1 (U1): The minimum write speed reaches 10MB/s. Comparing with class 10, many dash cams and DSLR cameras prefers U1 type. As the UHS bus interface provides a sustained write performance, it is perfect for 1080P or 4K video recording.
   • UHS-3 (U3): minimum write speed at 30MB/s. High-end cameras or drones always take a U3 rated SD card. Regardless of a high write speed, its read can hit up to 104MB/s
3. Video Speed class – This is the latest feature to support higher video resolution. They are displaying in “V” symbol.
   • V30: minimum write speed at 30MB/s
   • V60: lowest writing speed of 60MB/s
   • V90: minimum write speed at 90MB/s

The importance of SD card classes

When purchasing SD cards, users firstly will check the speed, and then it is the capacity. With a faster writing or reading, a camera can shoot a larger number of photos per minute. Even you purchase a 128GB or 512GB SD card, the recoding time is slow if you ignore the speed. In addition, the parameter of devices must be checked prior to order SD card. As you need to confirm the speed range of your equipment, it will make sure a good performance.

1. High SD speed classes enhance your devices’ performance
   • Action photography normally shoots photo in RAW format, each image displays in 41 MP and occupies over 25MB. To avoid any delays on photo loading, U1 and U3 class are the best option.
2. Speed version tells the cost
   • Normally we can know the cost range of SD card by capacity and speed. However, high capacity not always deliver high cost if the speed is slow. For example, one 128GB SD card class 10 is much cheaper than U1 or U3 version. Therefore, the lowest price is hard to guarantee high speed.
3. Speed backward compatibility
   • Bulk memory cards are able to be backward compatible within its generation. For instance, you can use one SDHC card in SD version slot. The only difference is that the device will work at the slowest speed of memory card. Thus, if you use one U3 SD card in U1 slot, the fastest speed will be same as U1 standard.

SD speed classes for host device

In order to bring users convenience, devices suppliers will mark class symbol on their hosts. It indicates a minimum speed request; the equipment cannot work properly if you use lower speed.

1. Host device requests for Class 4 SD card: You can use SD speed at Class 4, 6 and class 10
2. Host device asks for UHS-1 SDHC Card: It means it supports UHS-1 or UHS-3 memory cards.

Device with Video speed class has the same rule request as above. Therefore, it is wiser to check these details prior to order any bulk SD cards.

Benefits from fast SD Cards

As if the devices can support high speed type, SD cards in fast speed offer a good performance. Let’s research into these benefits from different devices.

1. Game console such as Nintendo Switch: A good game experience is guaranteed if you use a faster card, which is helpful for games loading.
2. Cameras: Photographers prefer continuous shooting modes. As speedy cards can catch up with an efficient storing, it means numbers of photos can be shoot at once. Especially, when you use camera to take photo in 4K or 8K, a U3 SD or CFexpress card can record extreme high-resolution images.
3. 3D printer and Raspberry Pi: You can save lots of time if you get fast SD card using there.

Notes on purchasing SD memory cards

Obviously, the cost is more if you choose a large capacity and high speed card. However, the purchase instruction should follow up the requests of devices. For example, your GPS device tells class 4 workable for data recording, then class 4 SD card is good and cheap enough for supporting its performance. Likewise, if you are engaging in photography business, a large amount of data transfer is a must for daily job. In this way, you ‘d better consider SD cards in higher speed and larger capacity.

Conclusion

SD speed rating is a key parameter for measuring speed of writing and reading, normally it is expressed as megabytes per second. Class speed on cards is telling minimum speed of recording, as if users know well of these specificat

The application of portable devices is growing sharply, therefore, the demands on accessible data storage also increase. SD card is not a single group, which has varied ranges available in size, class, interface, and specifications. The word “SD Card” represents a storage media including SD, SDHC and SDXC. Furthermore, it is just one type of bulk memory cards family, the size is the standard one. In order to create a right selection of SD card sizes, let’s start by understanding the use of SD card.

What does SD Card mean?

SD Card is a short term of secure digital card. It is one type of memory card developed by the SD Association. The main function of this media card is to store data such as documents, videos, photos, and the other contents. Also, it presently comes in three types indicating capacity ranges. There is SD, SDHC and SDXC. Standard SD cards go up to 2GB; SDHC represents the range of high capacity from 4GB to 32GB, and SDXC offers extended capacity from 64GB up to 2TB. Manufacturers also use sizes to define SD card capacity, in other words, we have SD card sizes from 128MB to 2TB.

Physical size of SD card

Bulk Memory cards have three major types following their physical size. SD cards are full size one, it is 32*24mm. Mini SD is another member and only half of it; Micro SD is the smallest one and is as small as a fingernail. To know all sizes and types of memory cards in details, let’s sort out as follow.

1.Secure Digital Cards (It includes three types)

• Size for Standard SD/SDHC/SDXC: 32mm*24mm (The physical size of these types is all same)
• Capacity: SD card is up to 2GB, SDHC supports from 4GB to 32GB, SDXC will be available from 64GB to 2TB

2.Micro SD Cards (same as SD offering three types)

• Size for Micro SD cards: 15mm*11mm (This dimension is same for all types)
• Capacity: Micro SD card – Up to 2GB, Micro SDHC – from 4GB to 32GB, Micro SDXC – from 64GB to 2TB

3. Mini SD Card

• Size: 21.5*20mm
• Capacity: Up to 2GB (As it is an old version, the available capacity is small)

Viewing the physical size can have an idea of the storage space. Obviously, SD card will need more rooms for installment. Thus, people use it often in DSLR cameras, tablets, 3D printers and the digital devices with enough spaces.

Labeling of SD Card

To distinguish SD cards in different capacities or specifications, manufacturers have use labels to tell information. As SD card delivers a standard dimension, it has a bigger space than Micro SD to present logo or the other description. Thus, you may find labels stick to the surface.

1.Capacity on the labels

• The density will be the number together with MB or GB, for instance, 8GB, 32GB and 128GB. These are indicating the capacity of SD cards

2.Speed on SD labels

• There are classes to tell speed. For example, you can find Class 4, class 6 and 10 there.  These are important data to tell the writing speed, which is 4MB/s, 6MB/s and 10MB/s by write.
• In addition, there are U1 and U3 also a guide for speed. In fact, U1 is identical to Class 10, but U1 means a minimum writing speed of 10MB/s; U3 requests the write not slower than 30 MB/s.
• Furthermore, the astonishing part is the speed of read. UHS-1 can reach up to 104MB/s by read, and UHS-II cards can hit 300MB/s. The structure of UHS-II card is a bit different, which has two rows of interface pins, this is the reason of high reading speed. Some SD labels will display the specific data of speed to expect good sales, so does SD card sizes.

3.Video speed

• UHS cards has a specific parameter for video shooting. There are V30, V60 and V90, which tells the minimum write speed at 30MB/s, 60MB/s and 90MB/s.

With the info of SD label, users can positively receive basic specification from it. Moreover, it can help people make right purchase.

Order appropriate SD card Capacity

Although users can understand basic info from labels, they are hard to make right purchase. Even there is no limit on budgets, the largest capacity may not fit the device. Prior to order SD cards, it is important to know capacity options in the market. What’s more, it is essential to check with the parameters of your equipment.

1. Old cameras: They only can support up to 32GB in SDHC
2. Latest smart phones: They can use up to 2TB

Therefore, getting the most appropriate SD card is the right way to make purchase.

Besides it, we need to research out the performance of SD card.

1. SD card in high capacity: it normally adopts TLC flash, which delivers fast speed but short lifespan.
2. SD card in low capacity: it uses SLC and MLC flash that helps extend life circle.

At present, the resolution of video and photo is reaching 4K and 8K, it requests one SD card in larger size and higher speed. Thus, 64GB is a basic choice; or you can go for 128GB and 1TB instead as if you have enough budgets.

All in all, selecting SD card sizes is following your actual needs and the requirement of devices. In case you have no idea of the status of equipment, you can collect 8gb, 32GB and 64GB SD cards to test. You will know the right SD card when the device can work after connection with this storage media.

Format size of SD card

Every SD card has file system, this is different from capacity by capacity.

• Format FAT: 4GB or smaller one
• Allocation unit size: 16KB
• FAT 32: from 8GB up to 64GB
• Allocation unit size: 32KB
• EXFAT: supports 64GB or above
• Allocation unit size: 128KB
• NTFS: from 64GB to 2TB

In fact, SD card performance is a bit affected by allocation unit. As you need to select default allocation unit size when formatting, the selection is linking to the density.

Small allocation unit sizes will take more time for data accessing, but large unit sizes can cause more waste. So proper use on unit sizes can bring efficiency on application. For instance, you can go for small size if you just load a few files. However, a large allocation size could be helpful for improving reading and writing if you need store video or films.

Final thought

The performance of SD card is directly affecting by various aspects such as size, speed, file system, video captures and flash type. To purchase a perfect card for photography or any institution, it is wise to know about these factors before any wholesale purchase.