What is the maximum speed that my computer can use when reading and writing to an SD card in the SD card slot?
Macs that use the USB bus to communicate with the SD card slot have a maximum speed of up to 480 Mbit/s. Newer Macs use the PCIe bus to communicate with the SD card slot and can transfer data at a much faster rate.
Check the packaging that came with your SD media to determine the maximum transfer rate used by that specific card.
Determine the maximum speed of your Mac using the System Profiler:
Choose About this Mac from the Apple () menu.
Click More Info.
Select USB from the hardware section (for Macs that use the USB bus to communicate with the SD card slot).
Select Internal Memory Card Reader and look for the Speed entry.
or
Select Card Reader from the Hardware section (for Macs that use the PCIe bus to communicate with the SD card slot).
Look for the Link Speed entry. Computers that use the PCIe bus express their speed as GT/s.
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