The SD memory card stands for Secure Digital Memory Card or the so-called SD card. SD cards are used to save digital photos or videos. I’m sure everyone is familiar with SD cards and how they work. However, do you know how to select a proper SD card when there are a variety of SD cards for you to choose from? And you may also wonder why there is a considerable price difference between two SD cards in which the brand and Capacity are the same.
There are two essential specifications to identify the SD cards: "Capacity" and "Writing Speed." The Capacity is like a bucket. The larger the bucket, the more water you can put in. So, the larger the capacity, the more data, you can put in. And the write speed is like a water pipe for watering. The faster the write speed (the thicker the pipe diameter), the quicker the water can be filled into the bucket.
The Capacity of SD Card
There are three types of SD memory cards: SD Standard, SD High Capacity, and SD eXtended Capacity according to the difference between the capacities. The Capacity of SD is too small to meet the storage requirement of digital images nowadays. On the other hand, the SDHC and SDXC are the more common and practical capacity specifications.
What is the main difference between the SDHC and SDXC memory cards with the same Capacity? The answer is that they support different file systems. The SDHC card supports the FAT32 file system. The Maximum Capacity of individual files is limited to 4GB only if you shoot a video with an SDHC card. If the file reaches 4GB, it will create another new file for continuous recording. In other words, the 32GB video will be divided into eight individual files under the FAT32 system. The SDXC card supports the exFAT file system, which allows a non-stop video recording until the memory card is full.
The Write Speed of SD Card
Regarding the operating speed of the SD card, it includes "writing" and "reading" speed. The reading and writing speed of SD cards keep increasing. The read speed of an SD card is more related to "Photography." The faster the reading speed is, the shorter the waiting time for playback.
A high writing speed SD card not only allows photographers to refill the buffers when firing a rapid burst of images. The high writing speed SD card is beneficial to the sports and wildlife photographers engaged in high-speed photography. Additionally, a high writing speed SD card supports the high frame rate on 4K or even 8K video shooting. If the writing speed of the SD card is too slow, the SD card may lose some of the video frames, which causes the video can not to play smoothly.
There are three different speed indicators: C, U, and V. The larger the number after the English characters, the faster the writing speed. The numbers after C are C1 to C10, and the numbers after U are U1 to U3. "V" is for the video shooting. The numbers after V are V30, V60, V90. The V30 means the writing speed is 30 MB/s, V60 means the writing speed is 60 MB/s, and V90 implies that the write speed is 90 MB/s.
Take two SD memory cards which are shown below, for example. Both of the SD cards have 32GB capacity. The SD card on the left indicates the speed is 120 MB/s, and the one on the right is 95 MB/s. Some people may think the SD card on the left is faster, but the 120 MB/s and 95 MB/s mean the reading speed. The writing speed is marked in the lower right corner. The SD card on the left is marked with U1 and Class10, indicating that the minimum reading speed is 10 MB/s. And the SD card on the right is marked with U3, Class10, indicating that the minimum reading speed is 30 MB/s, which is three times faster than the SD card on the left.
The writing and reading speed of the SD card is expressed in MB/s (Megabytes)/second, while the writing speed of the camera is expressed in Mb/s (Megabits)/second. Please note that MB/s and Mb/s are different units. And 8Mb is equal to 1MB. For instance, when the user sees the camera indicates that the writing speed is 200Mb/s, equivalent to 25MB/s. Therefore, the user has to select the SD card with the minimum writing speed of V30 or U3 to support the 200Mb/s writing speed of the camera. However, if users shoot 4K or even 8K video with a high frame rate, it is necessary to use a V60 SD memory card to write every frame into the SD card completely.
What is a Recording Length Per SD Card Capacity?
"Image Resolution" and "Frame Rate" are the two essential factors determining the file size. The higher the resolution comes with, the higher the frame rate. Because more data information is included in the high-resolution video, thus the video file is more significant. Take a 30fps video for example. If the resolution is Full HD (1920*1080), a 32GB SD card can record for about 4 hours; if the resolution is up to 4K, the 32GB SD card can only record for 1 hour.
How Many Photos Can Be Stored on an SD Card?
Each photo has a different file size according to exposure, color, and ISO information. The following table is a reference for the number of images that can be stored on an SD card. The actual stored numbers could vary depending on the real situation.
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