Memory cards real speed

This will be a short blog post about real speed of few different memory cards. You should know that it is not easy to find memory cards real speed. Manufacturers often put maximal speed on the package. With the notice that speed is not always achievable. My experience is that those speeds are true, but often, you only have reding speed. Reading speed is not important as much as writing speed. Unless backup is more important than actually recording. You always can wait a little bit to copy a memory card. But slow writing speeds will mean no recording at all in case of video. Or spending too much time buffering while photographing a sport, for example.

Classes of memory cards speed can give you guaranteed performance, which is good. But memory cards can often be much faster than class specification. So it is good to know real writing speed of memory card. Because even older, but fast memory card at the time can be used for many generations of cameras ahead.

Megabits and megabytes

Do not be confused with megabits (Mb) and megabytes (MB). I am seeing this a lot. We need fast cards for 4k video recording in most cases. Manufacturers are using megabits to tell us bitrate of the video, which is standard. But memory card and storage industry generally using megabytes to tell us speed. A bit is 8 times smaller than a byte, thus megabit is 8 times smaller then megabyte. So you need to divide camera specification by eight to find out if some card is fast enough. Or vice verse, we need to multiply card speeds by eight. Many consumer 4k cameras using 100 megabits for video. Even today you will hardly find memory card with 100 written on the package. But we do not need 100 megabytes per second, we need 100 megabits or 100/8=12.5 megabytes per second. And many cards are fast enough.

I used CrystalDiskMark to check memory cards real speed. In case of memory cards speed, you will get same results with all benchmark software. If you test storage for the system and very small files, results can vary depending on the software. But in case of photos, video, and audio, we have stable, compressed, big files. These kind of files are pulling most speeds from any storage solution. So you should look for biggest write and read number on this screenshots. That numbers will represent media files handling.

Benchmarking memory cards real speed

You can also have the limitation of the connected interface, like USB or Thunderbolt. In my case, USB 3.0 limitation was only for reading speeds of CFast cards, because this cards can read close to 500 MB/s. This shows real-life scenario because many of us only have USB 3.0 as a fastest port. Memory slot bus inside the camera can also be a limitation. Because some cameras can use only part of the speed of very fast cards. If you use regular HDD or older SSD, you can expect that computer storage will be slower than latest fastest memory cards.

memory cards real speed - CFast 2.0 Transcend 256GB CFX600
CFast 2.0 Transcend 256GB CFX600
CF SanDisk 64GB Extreme Pro
CF SanDisk 64GB Extreme Pro
SD SanDisk 64GB Extreme Pro
SD SanDisk 64GB Extreme Pro
SD Transcend 64GB UHS-1 (Speed Class 3)
SD Transcend 64GB UHS-1 (Speed Class 3)
microSD SanDisk 64GB Extreme - frist card
microSD SanDisk 64GB Extreme – first card
microSD SanDisk 64GB Extreme - second card
microSD SanDisk 64GB Extreme – second card
microSD Samsung 32GB Evo Plus
microSD Samsung 32GB Evo Plus


I have done memory cards real speed test on Windows computer with USB 3.0. I am receiving in some cases slower speeds on iMac. It was due card reader because I am sure I was getting better speeds with my previous card reader. On Windows, speeds are as it should be from these cards. And I am getting same speeds from Transcend CFast 256GB cards on both iMac and Windows. Thanks to the different card reader. For other cards, I am using a generic card reader which never give me a single problem. I believe my previous Kingston FCR-HS3 card reader was slightly faster with very fast memory cards on iMac. But it was sometimes unreliable. So I change it.

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