info about different SD and Micro SD cards and their ratings Class 10 vs 6 vs 4; UHS-I and UHS-II; V60 and V90; and more.

Many cheap too-good-to-be-true SD cards are indeed not the rated size. See this article in MakeUseOf to spot fake ones. It discusses software you can use to see if the SD or TF card is not the size it claims to be: FakeFlashTest, H2testw, ChipGenius. What to do if you're stuck with a fake card (maybe you can determine its real size and use it or maybe you can fix it using DiskPart). All software is Windows.

From https://www.makeuseof.com/tag/5-mistakes-avoid-buying-next-microsd-card/

There are four SD card formats:

1. microSD: Has a capacity up to 2GB, and works in any microSD slot.
2. microSDHC: Has a capacity of more than 2GB and up to 32GB, and works in hardware that supports either SDHC and SDXC.
3. microSDXC: Has a capacity of more than 32GB and up to 2TB (although at the time of writing, 1TB is the largest available card), and is only supported in SDXC-compatible devices.
4. microSDUC: Supports cards up to 128TB, and will require a compatible device.

Speed Class

• Class 2: At least 2MBps.
• Class 4: At least 4MBps.
• Class 6: At least 6MBps.
• Class 10: At least 10MBps.

UHS Speed Class

• U1: A write speed of at least 10MBps.
• U3: A write speed of at least 30MBps.

Application Performance Class

• A1: Minimum random read speed of 1500IOPS; random write speed of 500IOPS.
• A2: Minimum random read speed of 4000IOPS; random write speed of 200IOPS.

Video Speed Class

• V6: Minimum write speed of 6MBps.
• V10: Minimum write speed of 10MBps.
• V30: Minimum write speed of 30MBps.
• V60: Minimum write speed of 60MBps.
• V90: Minimum write speed of 90MBps.

This diagram comes from MakeUseOf at the URL above.
The SD Card Association recommends U3 or better for 4K video. If your card's write speed is too slow, it will drop frames and produce stuttering video.

This info from https://www.makeuseof.com/tag/best-fastest-microsd-cards/

This information provided by ChatGPT 11/12/2024

To measure transfer speeds between your MacBook and various thumb drives, you can use benchmarking tools that provide detailed read and write speeds. Here are some effective methods and tools:

• About: Blackmagic Disk Speed Test is a popular, free utility for macOS users to measure the performance of external storage devices.
• How to Use:
  1. Download it from the Mac App Store.
  2. Open the application and select your thumb drive as the target disk.
  3. Click “Start” to begin the test, which will show both read and write speeds.
• Advantages: Simple and quick to use, with a clear display of read and write speeds. Good for comparison across different drives.
• 20241112: this is not working for thumb drives on my MacBook Pro. I selected a thumb drive and clicked Start; nothing happened.

• About: AJA System Test Lite is a popular benchmarking tool designed to measure the performance of storage devices, widely used by video professionals.
• How to Use:
  1. Download AJA System Test Lite from AJA’s website (it’s free).
  2. Select your thumb drive as the target and specify the test file size (1GB is a common choice).
  3. Start the test, which will show sequential read and write speeds.
• Advantages: Offers more configuration options than Blackmagic, allowing you to test different file sizes and formats.

• About: If you prefer a command-line approach, you can use the `dd` command in Terminal to measure read and write speeds.
• How to Use:
  1. Write Speed: Open Terminal and enter:
     time dd if=/dev/zero of=/Volumes/YourDriveName/testfile bs=1024k count=1024
     Replace YourDriveName with the name of your thumb drive.
  2. Read Speed: After creating the test file, enter:
     time dd if=/Volumes/YourDriveName/testfile of=/dev/null bs=1024k
  3. Interpretation: The time reported at the end shows how long the data transfer took, from which you can calculate the speed.
• Advantages: Flexible and works without any additional software.

• About: While Disk Utility on macOS doesn’t directly measure speed, it can help identify if the drive is connected at the correct speed.
• How to Use:
  1. Open Disk Utility and select your thumb drive.
  2. Go to Info to see if it’s connected at USB 3.2 speeds or lower.
• Advantages: Useful for troubleshooting connectivity issues or confirming connection speed, though it won’t directly show transfer rates.

Using any of these methods will give you a good idea of your thumb drives’ actual read and write speeds. Blackmagic Disk Speed Test is usually the easiest for quick results, while the `dd` method in Terminal is a great way to measure without any added software.