How to really erase old files in my laptop?

[omigosh]

If you really want to be sure... replace the hard drive in it

 

[sysprog]

If you really want to be sure... replace the hard drive in it

That alone would of course not preserve any content; if it were done along with a correct backup and restore, it would be sufficient but not necessary.

 

[harborsparrow]

It turns out, Microsoft finally built in a utility for overwriting and clearing free space. And I've tried it and it seemed to work well. I learned about it from this article:

https://www.howtogeek.com/137108/how-securely-overwrite-free-space-in-windows/

The command is:

cipher /w:C:\

where C is the letter of the drive you want to securely overwrite the free space on.

Use a command prompt window with Administrative privileges.

Don't run anything else while it's going on. Expect it to take hours, possibly run it overnight.

 

[sysprog]

It turns out, Microsoft finally built in a utility for overwriting and clearing free space. And I've tried it and it seemed to work well. I learned about it from this article:

https://www.howtogeek.com/137108/how-securely-overwrite-free-space-in-windows/

The command is:

cipher /w:C:\

where C is the letter of the drive you want to securely overwrite the free space on.

Use a command prompt window with Administrative privileges.

Don't run anything else while it's going on. Expect it to take hours, possibly run it overnight.

It's not for SSDs.