Hello,

I am using Windows 10 and would like to know whether the system automatically checks and marks bad sectors in the hard drive so that data may never be written in them. Or is it necessary to install a program with which to check the drive periodically?

I think the hard-drive printed circuit board handles this; others can correct if I am in error.

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"Take care of thy backups and thy restores shall take care of thee." Ben Franklin revisited

Modern drives generally perform background scanning to identify potential defects. I don't know if Windows 10 does any pre-emptive testing, but the ATA standard provides a Write-Read-Verify feature which configures the drive to test each sector after writing to it.

Set Features subcommand 0Bh/8Bh enables/disables Write-Read-Verify. These changes are non-volatile, ie they persist after a power cycle. Obviously there will be a performance hit during writing.

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A backup a day keeps DR away.

Thank you for explaining how error checking is done. In case bad sectors are found, what their number should be for a free replacement of a hard drive before the expiration of the warranty?

Manufacturers have their own criteria for warranty RMA validation. For example, if any critical SMART attribute value falls below its threshold, then the drive will qualify for replacement. WD's drives typically allow for 500 bad sectors whereas Seagate's allow for 2500 or more.

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A backup a day keeps DR away.