high disk usage by applications

Recently I have noticed that my computer's hard disk is being written on by common application that would otherwise just operate on the RAM. I have checked my memory and there is more than enough space for common programmes like Chrome, Firefox to operate on. So I am not sure as to why those application are utilising the harddisk.

(I don't recall such problems until yesterday or the day before.)

What I did prior to problem:

• Uninstall Microsoft Update
• Changed BIOS settings
• Install an Intel driver for wireless adapter
• Changed Power plan

Status: I reversed all of that. Reinstall the update. Loaded default BIOS settings. Yet problem prevails.
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To this point, I had done a system restore, and scanned the computer with a third-party anti-virus software which detected a virus and has been removed. No further infections were detected.

My question(s) is:

• Is it normal for applications like browser, system services to constantly use the disk?

(I speculate they must be using the disk as RAM)​

• If it is not a normal routine, would you happen to know of a way to diagnose this problem further and perhaps a solution?

Thanks for your time!