While your success with running CHKDSK has improved your machine's present performance, any "new" errors appearing in subsequent runs of CHKDSK should be taken quite seriously as early warning of possible pending hard drive failure.
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In addition, the PCPitstop Full Tests still identifies significant disk fragmentation on your Hard Drive.
This can occur for a variety of reasons, and one reason that may be relevant in your case is the potential large files associated with onboard gaming, game expansion packs, and any saved movie media.
Files associated with gaming such as "Sims" are often quite large and may be difficult to defrag without more room on your hard drive or replacement with a larger hard.
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