From PC World: The SD Association is responsible for the further development of the SD memory card format. With a new SD Express standard, the transfer speeds for reading and writing to the small cards are to increase significantly. Specifically, SD Express version 9.1 stipulates that the memory cards must be connected via PCI Express 4.0 x1.
That change will double the speed of SD cards, which saw their most recent shakeup when the microSD Express standard debuted in February 2019.
The change to PCI Express 4.0 x1 increases the speed to a maximum of 1,969 megabytes per second. The previous connection with PCI-Express 3.0 x1 limited the speed to about 985 megabytes per second.
Buyers can identify the new SD cards by the “SD Express Speed Class” marking. In the future, there are also plans for a class that will use PCI Express 4.0 x2 and thus reach almost 4 gigabytes per second.
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