if you copying folder which have internally lots of files. than the speed goes down.

Second if you copying movies which have include sample , subtitles, info and screenshots files than also speed falling.

third when copying images than speed goes down.. always.

if you moving files than speed always goes fall. (Moving)

try to copy a big single file . Like a winrar. or zip file which have more than 3gb or 2 gb,

then test the speed . if it comes slow then try to copy in you internal hard drive the same file. like d drive to e drive , check the speed . if the speed comes slow.

then problem in your internal drive else in the External drive

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