Do you hear any noise from the drive? Scratching or click of death sorts of noises indicating a physical issue?
Generally my policy with drives is, if I have to ask if it is ok, it gets replaced. The suspect drive gets clearly market "suspect" in permanent marker across the top, and then it is forever used for movie storage and none-critical uses.
The speed of the read / write will be dependent on about a million different factors. Type of cache, code, location of data on platter, what has priority, and so on. Apart from any signs of physical issue with the drive, windows is most likly the cause the slow down.
You might also try booting in to the BIOS, and running SMART drive test to see what it says (if it shows there).
Still, my money is on windows. For every slow hard drive caused by a physical issue with the actual drive, there is about 10,000 computers that are just fine and being slowed down by windows and just appear to be running slow.
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