Why are USB 3 pen drives still slow (Though faster than USB 2)?

Sep 26, 2018
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USB 3.1 Gen 1 offers theoretical speed of 5 Gbps (640 MB/s). However my USB 3.0 pen drive when connected to Windows 7 PC USB 3 port shows max seq read speed of 150 MB/s and write speed of 60 MB/s. (Crystal Disk Mark test with 100MB datafile)

Is this normal or expected for a pen drive, even if it is USB 3 capable?

When can one get good USB 3 speeds? Does it depend upon the device itself?

e.g. the flash memory on USB 3 pen drive may be slower in operation even if it is connected to USB 3 port. Is it so?

Thanks.