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#21
An "unknown device" is many times a chipset driver...and it definitely could affect memory performance.
Go to the manufacturer's Support Downloads webpage for your exact computer model, install the full chipset download as Adminstrator. See if the unknown device goes away, and if the performance problems are solved.
If this is not the missing driver, check the other drivers in list to see which have their driver in Device manager. Often an Unknown Device driver is a card reader.